compliance: stop declaring V4L2_CAP_VIDEO_M2M capability

v4l2-compliance complains about "Video Capture cap set, but no Video
Capture formats defined" because V4L2_CAP_VIDEO_M2M is set and yet
vidioc_enum_fmt_cap implementation would simply return -EINVAL before
being ready for capturing.

V4L2 memory-to-memory operatons have never been actually supported. It
was introduced in an attempt to fix #67,
VIDIOC_G/S_PRIORITY test failures reported by v4l2-compliance, but
VIDIOC_G/S_PRIORITY is an exclusive feature when V4L2 file handle
framework is used, and this was certainly not the case until
#345 that brought in v4l2_fh for V4L2 Event API
support.

This change removes all declarations of M2M support.

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>

v4l2loopback.c

@@ -760,10 +760,6 @@ static int vidioc_querycap(struct file *file, void *priv,
 	cap->version = V4L2LOOPBACK_VERSION_CODE;
 #endif
 
-#ifdef V4L2_CAP_VIDEO_M2M
-	capabilities |= V4L2_CAP_VIDEO_M2M;
-#endif /* V4L2_CAP_VIDEO_M2M */
-
 	if (dev->announce_all_caps) {
 		capabilities |= V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT;
 	} else {
@@ -2251,9 +2247,6 @@ static void init_vdev(struct video_device *vdev, int nr)
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 7, 0)
 	vdev->device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT |
 			    V4L2_CAP_READWRITE | V4L2_CAP_STREAMING;
-#ifdef V4L2_CAP_VIDEO_M2M
-	vdev->device_caps |= V4L2_CAP_VIDEO_M2M;
-#endif
 #endif /* >=linux-4.7.0 */
 
 	if (debug > 1)