[XLA:Python] Add pytype_srcs and pytype_deps attributes to pytype_strict_library.
[XLA:Python] Add pytype_srcs and pytype_deps attributes to pytype_strict_library.

These attributes are ignored, because we don't use pytype in OSS builds at the moment.

While we're here, remove a copybara transformation that strips off a pytype_srcs attribute: we can just leave the attribute alone and it won't do any harm.
