Remove comment on merging stable branches -> main

[Saadnajmi]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

Back in #944 , I had added a comment about merging stable branches into our main branch. We have then since learned and documented that we shouldn't be doing that: main should merge to main, and stable should either have merges from upstream stable, or cherry picks.

Let's remove the comment, removing another diff from our repo.

Changelog

[Internal] [Removed] - Remove comment on merging stable branches -> main

Test Plan

Removing a comment, nothing should be affected.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	n/a	--

Base commit: e71b094
Branch: main