gn2bp: remove local protobuf includes via denylist

Adds a denylist for include dirs. The previous approach did not work as
not all targets listed protobuf as a dependency (some of them got
libprotobuf via genrule_shared_libs).

Test: //components/cronet/android:cronet
Change-Id: I05fb3f8206d5e7c904013d3da2fb7632a594177c