drm/amd/powerplay: remove defined but not used variables

Fix the following gcc warning:

drivers/gpu/drm/amd/amdgpu/../powerplay/hwmgr/vega10_powertune.c:710:46:
warning: ‘PSMGCEDCThresholdConfig_vega10’ defined but not used
[-Wunused-const-variable=]
 static const struct vega10_didt_config_reg
PSMGCEDCThresholdConfig_vega10[] =
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/hwmgr/vega10_powertune.c:654:46:
warning: ‘PSMSEEDCThresholdConfig_Vega10’ defined but not used
[-Wunused-const-variable=]
 static const struct vega10_didt_config_reg
PSMSEEDCThresholdConfig_Vega10[] =
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>