Clean up mixed builds module names filtering

* Remove `Bp2buildCcLibraryStaticOnlyList` it is never set
* Remove the rest of the sutff related to it
* Streamline MixedBuildsEnabled
* Rename BazelContext.BazelAllowlisted to BazelContext.NameFilter
  to reflect its action
* Rename bazelContext to mixedBuildBazelContext
* Fix minor warnings from Go static analyzer

Test: treehugger
Change-Id: Ie245c992f94bbfd5c7c23dd06917026200a28263