drm/amdgpu: Remove the MES self test

Remove MES self test as this conflicts the userqueue fence
interrupts.

v2:(Christian)
  - remove the amdgpu_mes_self_test() function and any now unused code.

Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>