dma-buf: cleanup kerneldoc of removed component

The seqno-fence was removed, cleanup the kerneldoc include as well.
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Fixes: 992c2381 ("dma-buf: nuke seqno-fence")
Link: https://patchwork.freedesktop.org/patch/msgid/20210901080002.5892-1-christian.koenig@amd.com

Documentation/driver-api/dma-buf.rst

@@ -176,12 +176,6 @@ DMA Fences Functions Reference
 .. kernel-doc:: include/linux/dma-fence.h
    :internal:
 
-Seqno Hardware Fences
-~~~~~~~~~~~~~~~~~~~~~
-
-.. kernel-doc:: include/linux/seqno-fence.h
-   :internal:
-
 DMA Fence Array
 ~~~~~~~~~~~~~~~