Remove blueprint.Module helper functions

Now that blueprint_go_binary modules are wrapped in a module type
that implements android.Module Soong should never see a blueprint.Module.
Remove the versions of the context methods that allow working with
blueprint.Modules.

Genrules still need VisitDirectDepsAllowDisabled, as they use a hack
that adds dependencies on host tools after the prebuilts mutators have
run, which means they may have a dependency on a disabled prebuilt
and need to manually forward it to the corresponding source module.

Test: all soong tests pass
Flag: EXEMPT refactor
Change-Id: I9147b450269749326e8fe75c5af310bd2d898d8c