Remove the `emit_swiftinterface` build setting

[brentleyjones]

This was only present to support Apple framework rules, but its design was flawed, so they no longer use it. Library evolution shouldn't be enabled for entire dependency subgraphs; authors of SDKs should explicitly enable it on their libraries with the library_evolution attribute.

PiperOrigin-RevId: 629786303 (cherry picked from commit 1ee51c8cc980e8e0a9cd7f21e99c5e424fbc3afa)

Cherry-pick notes: Applied the same change to the emit_private_swiftinterface build setting.