drm/amd/display: remove unused variables res_create_maximus_funcs and debug_defaults_diags

gcc with W=1 reports
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn20/dcn20_resource.c:1069:43: error:
  ‘res_create_maximus_funcs’ defined but not used [-Werror=unused-const-variable=]
 1069 | static const struct resource_create_funcs res_create_maximus_funcs = {
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn20/dcn20_resource.c:727:38: error:
  ‘debug_defaults_diags’ defined but not used [-Werror=unused-const-variable=]
  727 | static const struct dc_debug_options debug_defaults_diags = {
      |                                      ^~~~~~~~~~~~~~~~~~~~

These variables are not used so remove them.

Fixes: 25879d7b ("drm/amd/display: Clean FPGA code in dc")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>