Use localPool consistently for UseGoma() == true

Remove the distinction between pctx.StaticRule and
pctx.AndroidStaticRule so that all of the local rules correctly
get assigned to the localPool.  Also put Module and Singleton
rules into the localPool.

Test: compare out/soong/build.ninja
Change-Id: Id2bb38eff3c7209340fe55bc9006f00bd3661d81