Don't pass --legacy by default to aapt2 compile

Don't pass --legacy by default, it is rarely necessary and converts
some errors into warnings that crash at runtime.  The modules that
need it have had --legacy added to LOCAL_AAPT_FLAGS.

Bug: 135597368
Test: m java
Change-Id: I0cb213599d6612746d988b8966cbd529b5328db0