radeonsi: don't wait for shader compilation to finish when destroying a context

radeonsi: don't wait for shader compilation to finish when destroying a context

This was a hack for glsl_types deinitialization and it predates the proper
fix, which was the addition of glsl_type_singleton_decref.

This fixes a crash when the context is destroyed via the atexit handler.

Cc: 19.3 20.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3800>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3800>