init: remove last init.cpp global

By moving it into builtins.cpp..., but that's less bad than it is
now, especially since this is defunct in code targeting Q+.  Remove
the guards that init.h isn't being included by other files too as it's
not useful anymore.

Test: build
Change-Id: Ic564fcff9e8716ec924098b07a8c9d94ca25f960