Remove libnativehelper/include/nativehelper from include_dirs

Needed as libnativehelper is part of the runtime module and so will not
be present in an unbundled build, instead its build targets will be
provided as prebuilts.

Bug: 134379140
Test: m checkbuild
Change-Id: Ia3c7261b9b3f0d67a897af03ef6a3e016627b7e6