Remove Gemfile.lock from template (#33469)

Summary:
For the same reason we don't keep a yarn.lock or Podfile.lock, we shouldn't be keeping a Gemfile.lock in the template. The user will generate this on his own pulling in the current dependencies with the constraints in Gemfile. No need to lock to a specific version.

cc barbieri (author of https://github.com/facebook/react-native/pull/32303)
cc ravirajn22 (for raising the issue)

## Changelog

[iOS] [Fixed] - Remove Gemfile.lock from template

Pull Request resolved: https://github.com/facebook/react-native/pull/33469

Test Plan: no test plan

Reviewed By: javache

Differential Revision: D35074105

Pulled By: cortinico

fbshipit-source-id: 47d1b92329f1d55d4a0adbacbc7e5e45f9d957e0