drm/amd/display: Remove unused file

The file rv1_clk_mgr_clk.c is not used and for this reason useless. Drop
the unnecessary file.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>