Rename `assertWhenLegacyArchitectureMinifyingEnabled` to `assertLegacyArchitecture`

Summary:
This renames the method to be more aligned to the fact that we're using this entrypoint both for internal
and for OSS users.

I've also added a `assertLegacyArchitectureOnlyWhenMinifyEnabled` that will run only for internal builds.

Changelog:
[Internal] [Changed] -

Reviewed By: mdvacca

Differential Revision: D72389708

fbshipit-source-id: 23830df2f71cc816c7ca178b735a930e794efe47