Do not deallocate on Bitmap.recycle

Layoutlib only disposes the bitmap and doesn't recycle them. This causes
a double deallocation that triggers an assertion.
This change makes Bitmaps to be only freed when the finalizer is called.

Bug: http://b.android.com/203129
Change-Id: Ieabc1443544cfd2b4bf8ba9c8f9a4df8dd6e8220