grep can potentially run out of memory on Mac builds for large input
files. So we add a python util to handle filtering out files.

We will also need this util to filter plat_sepolicy.cil out of
product_sepolicy.cil

Bug: 119305624
Test: boot aosp_taimen
Change-Id: I61cd68f407ea5de43a06bf522a5fc149e5067e8c