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
