Make precompiled dalvik opt-in instead of opt-out

the address alignment issues that break skia in SkCanvas::drawRectCoords are a dealbreaker.

Set FORCE_PRECOMPILED_DALVIK to *anything* to play with the files, or to include them so that you can investigate and fix the issue.

Change-Id: Id07adc9b4c741a7916cab3705c92c9daaeca4e10
Revert "Don't wipe cache and dalvik"

The gains of this don't justify the means.
Especially with us playing with swapping in prebuilt libdvms.
Additionally, I'm fairly sure that this was preventing a fix for a crash caused by the BatteryTracker class in f/b from taking effect.

This reverts commit d8436b0c394f86da79248701917da75b4581ccad.

Change-Id: I863a11864ec8b8d1f74d02651b00ac76b93cb394
Merge "Revert "Don't wipe cache and dalvik"" into kk44