bp2build: remove header globs in generated srcs.

Not needed anymore for bp2build-incremental since https://android-review.googlesource.com/q/topic:no-include-check.

Not needed for mixed builds either, since cc compile actions aren't sandboxed.

Fixes: 186488830
Test: treehugger and go tests

Change-Id: Ib5d4908dcce6bf910a653c457bb251d726e717d4