Morphosyntax: avoid requesting unavailable MWT models

[antecedent]

Hi!

I tried the morphotag pipeline on Lithuanian (lit or lt) and bumped into an instance of Stanza's UnsupportedProcessorError that said the following:

Processor mwt is not known for language lt. If you have created your own model, please specify the mwt_model_path parameter when creating the pipeline.

Given that it is certainly not just Lithuanian that will trigger this error with no justifiable reason, could I propose checking with Stanza's resources.json instead of manually maintaining a list of all languages without a MWT model?

Note: it is not really "instead of" but "alongside" the manually curated list for the purposes of this PR, because I could not safely assume that all of MWT models that had been deemed unnecessary here were actually absent from Stanza's standard repository. Perhaps there had been unrelated reasons to exclude them?

[Jemoka]

Thanks! This is super helpful. Will merge in a few days after testing.