drm/amd/display: remove unused definition

drm/amd/display: remove unused definition

Eliminate the following warnings:
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_resource.c:1356:43: warning: unused variable 'res_create_maximus_funcs'
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_resource.c:894:38: warning: unused variable 'debug_defaults_diags'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=5296
Fixes: 25879d7b4986 ("drm/amd/display: Clean FPGA code in dc")
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>