glsl/tests: automake: cleanup all artefacts during clean-local

glsl/tests: automake: cleanup all artefacts during clean-local

With later commits we'll fix the generators to produce the files in the
correct location. That in itself will cause an issue since the files
will be left dangling and make distcheck will fail.

v2: Use -r only as needed (Eric)

Cc: Matt Turner <mattst88@gmail.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org> (v1)
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>