drm/radeon: remove r600_blit_shaders.[c|h]

The only use of the global variables in r600_blit_shaders.c
were in the old drivers/gpu/drm/radeon/r600_blit.c
This file was removed in
commit 8333f607 ("drm/radeon: remove UMS support")

So remove the r600_blit_shaders.[c|h] files

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>