dma-buf: Remove unused sync_dump()

sync_dump() is an unused, unexported, function that adds 64k to the
kernel image and doesn't even provide locking around the global array it
uses.

add/remove: 0/2 grow/shrink: 0/0 up/down: 0/-65734 (-65734)
Function                                     old     new   delta
sync_dump                                    198       -    -198
sync_dump_buf                              65536       -  -65536

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190419181904.6199-1-chris@chris-wilson.co.uk