media/gpu: Remove V4L2_EVENT_SRC_CH_PIXELFORMAT

There is no driver actually generating events with this flag set.
Since this is just downstream technical debt, which apparently isn't
really needed and makes it impossible to compile Chromium with V4L2JDA
enabled with upstream kernel headers, it's probably better to remove
this flag.

Bug: 942415
Test: Compile tested only (removing dead code).
Change-Id: I3803d622d384e8e3831c201812a14c919e5bb4dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1981412Reviewed-by: Ricky Liang <jcliang@chromium.org>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Auto-Submit: Sergey Senozhatsky <senozhatsky@chromium.org>
Commit-Queue: Sergey Senozhatsky <senozhatsky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#730073}

media/gpu/v4l2/v4l2_mjpeg_decode_accelerator.cc

@@ -762,8 +762,7 @@ bool V4L2MjpegDecodeAccelerator::DequeueSourceChangeEvent() {
   if (device_->Ioctl(VIDIOC_DQEVENT, &ev) == 0) {
     if (ev.type == V4L2_EVENT_SOURCE_CHANGE) {
       VLOGF(2) << ": got source change event: " << ev.u.src_change.changes;
-      if (ev.u.src_change.changes &
-          (V4L2_EVENT_SRC_CH_RESOLUTION | V4L2_EVENT_SRC_CH_PIXELFORMAT)) {
+      if (ev.u.src_change.changes & V4L2_EVENT_SRC_CH_RESOLUTION) {
         return true;
       }
       VLOGF(1) << "unexpected source change event.";