drm/amdgpu/pp: remove the get_temperature API

This is also supported with the read_sensor API and there
were no more users of the get_temperature API.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>