radeon: remove left over dead code

Fixes: 4e0d99a6 "r100: Use shared debug code"
Cc: Pauli Nieminen <suokkos@gmail.com>
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
(cherry picked from commit eee8dd7c)