Skip building compat files if REL

In release build, we don't need to (and shouldn't) build compat files,
because it doesn't make sense to build compat files for itself.
Currently this didn't happen because REL build only happens on -dev
branches. To support main branch setting REL, filtering out
PLATFORM_SEPOLICY_VERSION from compat versions list.

Bug: 296780580
Test: build with next
Change-Id: Ia5c09a1c9b4209ed82dc66307d57decb4f442477