chore(firefox): kill original puppeteer-firefox tests (puppeteer#4047)

When we started working on Puppeteer-Firefox, we forked original
Puppeteer testsuite.

This patch concludes the effort to merge testsuites back together.

Fixes puppeteer#3889

experimental/puppeteer-firefox/package.json

@@ -13,9 +13,6 @@
   },
   "scripts": {
     "install": "node install.js",
-    "unit": "node test/test.js",
-    "funit": "cross-env DUMPIO=1 PRODUCT=firefox node test/test.js",
-    "cunit": "cross-env PRODUCT=chromium node test/test.js",
     "tsc": "tsc -p ."
   },
   "author": "The Chromium Authors",
@@ -28,27 +25,5 @@
     "progress": "^2.0.1",
     "proxy-from-env": "^1.0.0",
     "rimraf": "^2.6.1"
-  },
-  "devDependencies": {
-    "puppeteer": "^1.11.0",
-    "@pptr/testrunner": "^0.5.0",
-    "@pptr/testserver": "^0.5.0",
-    "@types/debug": "0.0.31",
-    "@types/extract-zip": "^1.6.2",
-    "@types/mime": "^2.0.0",
-    "@types/node": "^8.10.34",
-    "@types/rimraf": "^2.0.2",
-    "@types/ws": "^6.0.1",
-    "commonmark": "^0.28.1",
-    "cross-env": "^5.0.5",
-    "eslint": "^5.9.0",
-    "esprima": "^4.0.0",
-    "jpeg-js": "^0.3.4",
-    "minimist": "^1.2.0",
-    "ncp": "^2.0.0",
-    "pixelmatch": "^4.0.2",
-    "pngjs": "^3.3.3",
-    "text-diff": "^1.0.1",
-    "typescript": "3.1.6"
   }
 }