enable aapt for unbundled builds

It was available for unbundled builds when the build rules were in mk form and aapt2 is enabled for unbundled, so there's not a strong reason why aapt should be disabled for unbundled build

Change-Id: I6589eafbe8d2e423c9ac925b3614763fa6a511ac
Fixes: 217747798
Test: local compile