mesa: Use _mesa_detach_renderbuffer when deleting a texture

mesa: Use _mesa_detach_renderbuffer when deleting a texture

The functional change is that now invalidate_framebuffer is called if
the texture is actually detached from one of the currently bound FBOs.
Previously this was only done for renderbuffers.

The remaining changes make the texture delete path look more similar to
the renderbuffer delete path.  This includes adding relevant spec
quotations to justify the behavior.

Fixes piglit fbo-incomplete "delete texture of bound FBO" test.

v2: Move 'fb->Attachment[i].Texture == att' check from previous patch to
this patch... where it was intended to be in the first place.  Noticed
by Chad.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Cc: "9.2" <mesa-stable@lists.freedesktop.org>