Update to only apply experimental process.env stub in development

[ijjk]

This updates to not modify process.env in production mode as weren't changing the behavior with the stub there yet anyways and were only adding the stub to warn in development mode initially. We plan to make the stub only apply to files outside of node_modules in a follow-up PR

x-ref: #11893

[ijjk]

Stats from current PR

Default Server Mode (Decrease detected ✓)

General Overall decrease ✓

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
buildDuration	11s	10.8s	-199ms
nodeModulesSize	55.6 MB	55.6 MB	-7 B

Page Load Tests Overall decrease ⚠️

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
/ failed reqs	0	0	✓
/ total time (seconds)	1.819	1.903	⚠️ +0.08
/ avg req/sec	1374.65	1313.92	-60.73
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	0.918	0.947	⚠️ +0.03
/error-in-render avg req/sec	2723.16	2639.56	-83.6

Client Bundles (main, webpack, commons)

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
main-HASH.js gzip	6.25 kB	6.25 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
de003c3a9d30..5e5e.js gzip	10.3 kB	10.3 kB	✓
framework.a1..NSE.txt gzip	220 B	220 B	✓
framework.a1..NSE.txt gzip	220 B	220 B	✓
framework.HASH.js gzip	39 kB	39 kB	✓
Overall change	56.7 kB	56.7 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
main-HASH.module.js gzip	4.79 kB	4.79 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
de003c3a9d30..dule.js gzip	6.85 kB	6.85 kB	✓
framework.HA..dule.js gzip	39 kB	39 kB	✓
Overall change	51.4 kB	51.4 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
polyfills-HASH.js gzip	26.2 kB	26.2 kB	✓
Overall change	26.2 kB	26.2 kB	✓

Client Pages

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_app.js gzip	1.23 kB	1.23 kB	✓
_error.js gzip	3.12 kB	3.12 kB	✓
hooks.js gzip	663 B	663 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	2.06 kB	2.06 kB	✓
routerDirect.js gzip	280 B	280 B	✓
withRouter.js gzip	278 B	278 B	✓
Overall change	7.85 kB	7.85 kB	✓

Client Pages Modern

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_app.module.js gzip	598 B	598 B	✓
_error.module.js gzip	2.09 kB	2.09 kB	✓
hooks.module.js gzip	383 B	383 B	✓
index.module.js gzip	223 B	223 B	✓
link.module.js gzip	1.52 kB	1.52 kB	✓
routerDirect..dule.js gzip	279 B	279 B	✓
withRouter.m..dule.js gzip	278 B	278 B	✓
Overall change	5.37 kB	5.37 kB	✓

Client Build Manifests

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Rendered Page Sizes

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
index.html gzip	929 B	929 B	✓
link.html gzip	939 B	939 B	✓
withRouter.html gzip	927 B	927 B	✓
Overall change	2.79 kB	2.79 kB	✓

---

Serverless Mode (Decrease detected ✓)

General Overall decrease ✓

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
buildDuration	11.4s	11.5s	⚠️ +5ms
nodeModulesSize	55.6 MB	55.6 MB	-7 B

Client Bundles (main, webpack, commons)

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
main-HASH.js gzip	6.25 kB	6.25 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
de003c3a9d30..5e5e.js gzip	10.3 kB	10.3 kB	✓
framework.a1..NSE.txt gzip	220 B	220 B	✓
framework.a1..NSE.txt gzip	220 B	220 B	✓
framework.HASH.js gzip	39 kB	39 kB	✓
Overall change	56.7 kB	56.7 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
main-HASH.module.js gzip	4.79 kB	4.79 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
de003c3a9d30..dule.js gzip	6.85 kB	6.85 kB	✓
framework.HA..dule.js gzip	39 kB	39 kB	✓
Overall change	51.4 kB	51.4 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
polyfills-HASH.js gzip	26.2 kB	26.2 kB	✓
Overall change	26.2 kB	26.2 kB	✓

Client Pages

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_app.js gzip	1.23 kB	1.23 kB	✓
_error.js gzip	3.12 kB	3.12 kB	✓
hooks.js gzip	663 B	663 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	2.06 kB	2.06 kB	✓
routerDirect.js gzip	280 B	280 B	✓
withRouter.js gzip	278 B	278 B	✓
Overall change	7.85 kB	7.85 kB	✓

Client Pages Modern

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_app.module.js gzip	598 B	598 B	✓
_error.module.js gzip	2.09 kB	2.09 kB	✓
hooks.module.js gzip	383 B	383 B	✓
index.module.js gzip	223 B	223 B	✓
link.module.js gzip	1.52 kB	1.52 kB	✓
routerDirect..dule.js gzip	279 B	279 B	✓
withRouter.m..dule.js gzip	278 B	278 B	✓
Overall change	5.37 kB	5.37 kB	✓

Client Build Manifests

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Serverless bundles

	zeit/next.js canary	ijjk/next.js update/env-stubbing	Change
_error.js	558 kB	558 kB	✓
404.html	4.18 kB	4.18 kB	✓
hooks.html	3.81 kB	3.81 kB	✓
index.js	558 kB	558 kB	✓
link.js	595 kB	595 kB	✓
routerDirect.js	587 kB	587 kB	✓
withRouter.js	587 kB	587 kB	✓
Overall change	2.89 MB	2.89 MB	✓