drm/amdgpu: remove AMDGPU_NUM_SYNCS

Just a leftover from semaphores.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>