Decruft flowconfig

Summary:
* Use `;` instead of `#` for comments because IDEs treat these files are `ini` syntax, and thus by default use `;` for comments. Flow supports both `;` and `#`.
* Fix line lengths and remove trailing comment periods.
* When possible, prefer `<PROJECT_ROOT>`  over `*./`.
* Be more specific with certain ignores.
* Remove ignores to modules that don't exist anymore or no longer have issues.
* `class_static_fields` and `class_instance_fields` are enabled by default starting with flow 0.33.0.

Reviewed By: gabelevi

Differential Revision: D4164031

fbshipit-source-id: 7e4b1b91837a675fa7c5a0bb75ec869c5b23f8bb

.flowconfig

@@ -1,29 +1,24 @@
 [ignore]
-
-# We fork some components by platform.
+; We fork some components by platform
 .*/*[.]android.js
 
-# Ignore templates with `@flow` in header
-.*/local-cli/generator.*
+; Ignore generators because they are not real JS files
+.*/local-cli/generator/templates/.*
 
-# Ignore malformed json
-.*/node_modules/y18n/test/.*\.json
-
-# Ignore the website subdir
+; Ignore the website subdir
 <PROJECT_ROOT>/website/.*
 
-# Ignore BUCK generated dirs
+; Ignore "BUCK" generated dirs
 <PROJECT_ROOT>/\.buckd/
 
-# Ignore unexpected extra @providesModule
-.*/node_modules/commoner/test/source/widget/share.js
+; Ignore unexpected extra "@providesModule"
 .*/node_modules/.*/node_modules/fbjs/.*
 
-# Ignore duplicate module providers
-# For RN Apps installed via npm, "Libraries" folder is inside node_modules/react-native but in the source repo it is in the root
+; Ignore duplicate module providers
+; For RN Apps installed via npm, "Libraries" folder is inside
+; "node_modules/react-native" but in the source repo it is in the root
 .*/Libraries/react-native/React.js
 .*/Libraries/react-native/ReactNative.js
-.*/node_modules/jest-runtime/build/__tests__/.*
 
 [include]
 
@@ -34,9 +29,6 @@ flow/
 [options]
 module.system=haste
 
-esproposal.class_static_fields=enable
-esproposal.class_instance_fields=enable
-
 experimental.strict_type_args=true
 
 munge_underscores=true