Back out "Apply Babel arrow transform only when needed" (facebook#41282)

Summary:
Pull Request resolved: facebook#41282

Original commit changeset: ad96540bb777

Original Phabricator Diff: D50818568

Changelog: [Internal]

Reviewed By: robhogan

Differential Revision: D50885400

fbshipit-source-id: b5039b6430e48a3b87456758bf4fef6cc182ee8f

packages/react-native-babel-preset/src/configs/main.js

@@ -84,9 +84,10 @@ const getPreset = (src, options) => {
     extraPlugins.push([require('@babel/plugin-transform-classes')]);
   }
 
-  if (!isHermes && (isNull || src.indexOf('=>') !== -1)) {
-    extraPlugins.push([require('@babel/plugin-transform-arrow-functions')]);
-  }
+  // TODO(gaearon): put this back into '=>' indexOf bailout
+  // and patch react-refresh to not depend on this transform.
+  extraPlugins.push([require('@babel/plugin-transform-arrow-functions')]);
+
   if (!isHermes) {
     extraPlugins.push([require('@babel/plugin-transform-computed-properties')]);
     extraPlugins.push([require('@babel/plugin-transform-parameters')]);