Remove special-casing of DCLA libraries

This is a revert of aosp/2449906

mixed build currently supports platform and apex variants of allowlisted
cc libraries. However when building apex variants, we would pass an
apexKey only for allowlisted _dcla_ libraries. This meant that for libraries in
mixed build allowlist but not in dcla allowlist, Soong's apex variants
were being replaced with Bazel's platform variants.

Bug: 270339610
Bug: 288906815
Test: Added libnativeloader, libartpalette-system to prod mixed build
allowlist and `m`

Change-Id: I922fed898b3c3961466cd1165c371839a4192237