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 aaptflags.

Bug: 135597368
Test: m java
Change-Id: Ib05a07ead4084dd32ba28df26708d81bb53f2f2a