Stopgap fix to avoid aapt2 build errors.

Should fix build errors on mainline_modules on aosp-master. This script
still does not propagate all options to aapt2 correctly, but that will
be fixed by removing the script altogether (b/174315599).

Test: build/soong/scripts/build-aml-prebuilts.sh art-module-sdk \
      art-module-test-exports conscrypt-module-host-exports \
      conscrypt-module-sdk conscrypt-module-test-exports \
      i18n-module-host-exports i18n-module-sdk \
      i18n-module-test-exports platform-mainline-sdk \
      platform-mainline-test-exports runtime-module-host-exports \
      runtime-module-sdk
  (the failing command in
  build/soong/scripts/build-mainline-modules.sh)
Bug: 175386777
Change-Id: I81aa20b1abd177f0d2886ab9b04831437da72f2a