udmabuf: Remove deleted map/unmap handlers.

Commit 7f0de8d8 ("dma-buf: Drop dma_buf_k(un)map") removed map/unmap
handlers, but they still existed in udmabuf. Remove them there as well

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: 7f0de8d8 ("dma-buf: Drop dma_buf_k(un)map")
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191126142516.630200-1-maarten.lankhorst@linux.intel.com