meta: Drop the src == dst restriction on meta glBlitFramebuffer().

meta: Drop the src == dst restriction on meta glBlitFramebuffer().

From the GL_ARB_fbo spec:

    If the source and destination buffers are identical, and the
    source and destination rectangles overlap, the result of the blit
    operation is undefined.

As far as I know, that's the only thing that would have been of concern
for this.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>