Don't enforce <uses-library> checks if dexpreopt for apps is disabled.

Otherwise the check fails, as it depend on non-existent dexpreopt.config
files. This CL fixes broken build cf_x86_phone-userdebug_coverage.

Bug: 183931403
Bug: 132357300
Test: forrest build for cf_x86_phone-userdebug_coverage.
Change-Id: I6f977c1e0c2d2160b1813d2d1c36459f0641235e