drm/xe: Remove unseless xe_force_wake_prune.

(!(gt->info.engine_mask & BIT(i))) cases are already
handled in the init function. And these masks are not
modified between the init and the prune.

Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>