Remove unused @types dev dependencies

- dotenv
  - Types are included as of 8.2.0
  - motdotla/dotenv#430
- execa
  - Types are included as of 2.0.0
  - sindresorhus/execa#188
- nock
  - Types are included as of 11.3
  - nock/nock#1670

sdk/storage/storage-file-datalake/package.json

@@ -70,12 +70,9 @@
     "@azure/identity": "^1.0.0",
     "@microsoft/api-extractor": "^7.5.4",
     "@rollup/plugin-replace": "^2.2.0",
-    "@types/dotenv": "^6.1.0",
-    "@types/execa": "0.9.0",
     "@types/fs-extra": "^8.0.0",
     "@types/mocha": "^5.2.5",
     "@types/nise": "^1.4.0",
-    "@types/nock": "^10.0.1",
     "@types/node": "^8.0.0",
     "@types/query-string": "6.2.0",
     "@typescript-eslint/eslint-plugin": "^2.0.0",
@@ -158,4 +155,4 @@
       }
     ]
   }
-}
+}