Update stale 'Hermes V1' comments (#56757)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56757

Update comments that still say 'Hermes V1' as if it is an opt-in feature.
Since Hermes (formerly called Hermes V1) is now the only supported engine:
- hermes-engine.podspec: drop 'when using Hermes V1' from hermesc note
- PathUtils.kt: rewrite the hermesc path comment to drop the 'opted in to Hermes V1' phrasing
- hermes-engine/build.gradle.kts: 'Hermes V1 by default...' -> 'Hermes by default...'

## Changelog:
[Internal] -

Reviewed By: cortinico

Differential Revision: D104649634

fbshipit-source-id: 9b0a05ed013c7ba908c7abe467d5e3c1c3c2f26c