Remove stale Podfile flipper_post_install call

Since this is still calling scripts/cocoapods/flipper.rb:
Setting React-RCTAppDelegate > config.build_settings > FB_SONARKIT_ENABLED=1
Causing React/AppSetup/RCTAppSetupUtils.mm to wrongly try importing FlipperKit

Introduced in RN v0.62
- https://github.com/facebook/react-native/blob/v0.62.0/template/ios/Podfile
- #1586

We should have removed in RN v0.64
- https://github.com/facebook/react-native/blob/v0.64.0/template/ios/Podfile
- https://github.com/facebook/react-native/blob/v0.63.5/template/ios/Podfile

ios/Podfile

@@ -91,7 +91,6 @@ target 'MetaMask-QA' do
 end
 
 post_install do |installer|
-	flipper_post_install(installer)
   react_native_post_install(installer)
   __apply_Xcode_12_5_M1_post_install_workaround(installer)
 end