drm/i915: Remove dma_resv_prune

The signaled bit is already used for quick testing if a fence is signaled.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/460722/


Signed-off-by: Christian König <christian.koenig@amd.com>