Summary:
This PR is small cleanup in scripts in `rn-tester-e2e` package, it creates unified script so that we can easily pass platform as an argument. Context: https://github.com/facebook/react-native/pull/36267#discussion_r1269378065
## Changelog:
[INTERNAL] [CHANGED] - Unify `test-e2e` command in `rn-tester-e2e` package
Pull Request resolved: https://github.com/facebook/react-native/pull/38701
Test Plan: CI Green ✅
Reviewed By: NickGerleman, cipolleschi
Differential Revision: D47949821
Pulled By: cortinico
fbshipit-source-id: 90bbc96281e89dec505999ff5e51db7ca78da6dc
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