Assume a texture is unbound after deleting it

Bug #9316260

The GL specification indicates that deleting a bound texture has
the side effect of binding the default texture (name=0). This change
replaces all calls to glDeleteTextures() by Caches::deleteTexture()
to properly keep track of texture bindings.

Change-Id: Ifbc60ef433e0f9776a668dd5bd5f0adbc65a77a0