Update _gitignore - Remove .hprof (#31679)

Summary:
added .hprof file is generated when building a release apk and it's size is > 300 MB, and we don't want it to be in the repo

## Changelog

[General] [Changed] - Remove .hprof

Pull Request resolved: https://github.com/facebook/react-native/pull/31679

Reviewed By: yungsters

Differential Revision: D28967470

Pulled By: PeteTheHeat

fbshipit-source-id: 521f653428ebdd2a33fb251ce18c4faada53bf27