Cleanup flowconfig options in react-native (#57173)

Summary:
Pull Request resolved: #57173

- All legacy casting syntax has been converted, so we remove `casting_syntax=both` to use the default option of only allowing the new `as` casting syntax
- Removed all other options that are already the default value

Changelog: [Internal]

Reviewed By: panagosg7

Differential Revision: D108281827

fbshipit-source-id: 0557fd0e45061c5c3c1d2f517caa3491921d153d

Author: SamChou19815

.flowconfig

@@ -43,16 +43,8 @@ packages/react-native/interface.js
 packages/react-native/flow/
 
 [options]
-enums=true
-experimental.pattern_matching=true
-experimental.allow_variance_keywords=true
-casting_syntax=both
-component_syntax=true
-
 emoji=true
 
-exact_by_default=true
-
 format.bracket_spacing=false
 
 module.file_ext=.js