Just drop the default WP bitmap, don't explicitly recycle it

Recycling invalidates it out from under any client code that might
have retained the reference previously.  That's not sociable.

Just drop the internal cache reference.  The underlying storage will
be properly freed by GC if it's genuinely not being used anywhere
else.

Change-Id: I94e0e2ba2b78daa40c8026e6fc72fda3bed57ae3
Fixes: 79108131
Bug: 74534423
Test: atest android.content.cts.ContextWrapperTest#testAccessWallpaper