Remove unused dependencies from workspace root. (#13340)

Remove 'async', 'bundle-collapser', 'del', 'derequire', 'escape-string-regexp', 'git-branch', 'gzip-js',
'merge-stream', 'platform', 'run-sequence' & 'yargs'.

Most of them were used in the old Grunt build system.

This ends up removing 32 packages, according to yarn.lock.

package.json

@@ -6,7 +6,6 @@
   ],
   "devDependencies": {
     "art": "^0.10.1",
-    "async": "^1.5.0",
     "babel-cli": "^6.6.5",
     "babel-code-frame": "^6.26.0",
     "babel-core": "^6.0.0",
@@ -37,7 +36,6 @@
     "babel-preset-react": "^6.5.0",
     "babel-traverse": "^6.9.0",
     "babylon": "6.18.0",
-    "bundle-collapser": "^1.1.1",
     "chalk": "^1.1.3",
     "cli-table": "^0.3.1",
     "coffee-script": "^1.8.0",
@@ -46,9 +44,6 @@
     "create-react-class": "^15.6.3",
     "cross-env": "^5.1.1",
     "danger": "^3.0.4",
-    "del": "^2.0.2",
-    "derequire": "^2.0.3",
-    "escape-string-regexp": "^1.0.5",
     "eslint": "^4.1.0",
     "eslint-config-fbjs": "^1.1.1",
     "eslint-plugin-babel": "^3.3.0",
@@ -61,22 +56,18 @@
     "filesize": "^3.5.6",
     "flow-bin": "^0.72.0",
     "flow-coverage-report": "^0.4.0",
-    "git-branch": "^0.3.0",
     "glob": "^6.0.4",
     "glob-stream": "^6.1.0",
     "google-closure-compiler": "20180506.0.0",
-    "gzip-js": "~0.3.2",
     "gzip-size": "^3.0.0",
     "jasmine-check": "^1.0.0-rc.0",
     "jest": "^23.1.0",
     "jest-diff": "^23.0.1",
-    "merge-stream": "^1.0.0",
     "minimatch": "^3.0.4",
     "minimist": "^1.2.0",
     "mkdirp": "^0.5.1",
     "ncp": "^2.0.0",
     "object-assign": "^4.1.1",
-    "platform": "^1.1.0",
     "prettier": "1.13.7",
     "prop-types": "^15.6.2",
     "random-seed": "^0.3.0",
@@ -89,13 +80,11 @@
     "rollup-plugin-prettier": "^0.3.0",
     "rollup-plugin-replace": "^2.0.0",
     "rollup-plugin-strip-banner": "^0.2.0",
-    "run-sequence": "^1.1.4",
     "semver": "^5.5.0",
     "targz": "^1.0.1",
     "through2": "^2.0.0",
     "tmp": "~0.0.28",
-    "typescript": "~1.8.10",
-    "yargs": "^6.3.0"
+    "typescript": "~1.8.10"
   },
   "devEngines": {
     "node": "8.x || 9.x || 10.x"