drm/amd/pm: Delete non-functional SMU8 get_dal_power_level implementation

drm/amd/pm: Delete non-functional SMU8 get_dal_power_level implementation

This function was effectively a no-op because it always
returned the maximum possible power level, because the
maximum voltage is in millivolts while the dependency
table didn't contain actual voltages.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>