Revert^2 "remove libbinder_ndk_helper_headers"

This reverts commit 1f01c41f.

Reason for revert: broke NDK variant builds, which wasn't detected
due to incremental builds not reflecting sysroot removals.

Bug: 357711733
Test: clean builds work

Change-Id: I4170325b5d796f990259f6afc4ad7ae0fac01600