* Revert "fix for issue 3067"
This reverts commit 041b4b6723.
Fixes#3143. The original issue (#3067) was people trying to use
tts.tts_with_vc_to_file() with XTTS and was "fixed" in #3109. But XTTS has
integrated VC and you can just do tts.tts_to_file(..., speaker_wav="..."), there
is no point in passing it through FreeVC afterwards. So, reverting this commit
because it breaks tts.tts_with_vc_to_file() for any model that doesn't have
integrated VC, i.e. all models this method is meant for.
* fix: support multi-speaker models in tts_with_vc/tts_with_vc_to_file
* fix: only compute spk embeddings for models that support it
Fixes#1440. Passing a `speaker_wav` argument to regular Vits models failed
because they don't support voice cloning. Now that argument is simply ignored.