Remove the post install step (#28651)

Summary:
Removes the post install step for Flipper, as the latest version of YogaKit is compatible with swift 5.

cc alloy

## Changelog

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[Flipper] [Template] - Remove the post install step for Flipper
Pull Request resolved: https://github.com/facebook/react-native/pull/28651

Test Plan: Tested a newly created RN app without post install step and it built successfully.

Reviewed By: passy

Differential Revision: D21064653

Pulled By: priteshrnandgaonkar

fbshipit-source-id: da56d0754d918e30a0ebe480c77590f0139d48ac

scripts/react_native_pods.rb

@@ -88,14 +88,3 @@ def use_flipper!(versions = {})
   pod 'FlipperKit/FlipperKitLayoutTextSearchable', versions['Flipper'], :configuration => 'Debug'
   pod 'FlipperKit/FlipperKitNetworkPlugin', versions['Flipper'], :configuration => 'Debug'
 end
-
-# Post Install processing for Flipper
-def flipper_post_install(installer)
-  installer.pods_project.targets.each do |target|
-    if target.name == 'YogaKit'
-      target.build_configurations.each do |config|
-        config.build_settings['SWIFT_VERSION'] = '4.1'
-      end
-    end
-  end
-end

template/ios/Podfile

@@ -18,9 +18,6 @@ target 'HelloWorld' do
   # Note that if you have use_frameworks! enabled, Flipper will not work and
   # you should disable these next few lines.
   use_flipper!
-  post_install do |installer|
-    flipper_post_install(installer)
-  end
 end
 
 target 'HelloWorld-tvOS' do