dma-buf/dma_fence_array: remove unused functionality v4

dma-buf/dma_fence_array: remove unused functionality v4

Amdgpu was the only user of the signal on any feature and we dropped
that use case recently, so we can remove that functionality.

v2: update num_pending only after the fence is signaled
v3: separate out simplifying dma_fence_array implementation
v4: fix XE patch split fallout

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://lore.kernel.org/r/20260422103012.1647-1-christian.koenig@amd.com