Remove execmod support for newer API versions

Drop support for execmod (aka text relocations) for newer API versions.
Retain it for older app APIs versions.

Bug: 30146890
Bug: 20013628
Bug: 35323421
Test: policy compiles.
Change-Id: Ie54fdb385e9c4bb997ad6fcb6cff74f7e32927bb
3 files changed