openh264enc: fix broken header AU emission by base class

This encoder advertises alignment=au as output format, which means
each output frame should contain a full decodable access unit.

The video encoder base class is not aware of our output alignment
and will output spurious buffers with just the SPS/PPS inside when
we call gst_video_encoder_set_headers(), which is broken because
each buffer is supposed to contain a full decodable access unit
in our case.

Just don't tell the base class about our headers, they will be
sent at the beginning of each IDR frame anyway.

Part-of: <gstreamer/gst-plugins-bad!2478>
29 jobs for !2478 with backport-mr-2178-into-1.18-openh264-fix-sps-pps-header in 27 minutes and 45 seconds (queued for 11 seconds)
detached
Status Name Job ID Coverage
  Build Docker
passed alpine amd64 manifest builder docker #13085501

00:00:12

passed android docker #13085500

00:00:13

passed cerbero fedora amd64 docker #13085499

00:00:13

passed fedora amd64 docker #13085498

00:00:13

passed gst-indent amd64 docker #13085502

00:00:13

 
  Preparation
passed gst indent #13085504

00:00:24

passed manifest #13085503

00:00:29

 
  Build
passed build cerbero cross-android universal #13085513
gstreamer

00:06:49

passed build cerbero cross-ios universal #13085517
gst-ios-14.3

00:22:44

passed build cerbero cross win32 #13085514
gstreamer

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passed build cerbero cross win64 #13085515
gstreamer

00:04:43

passed build cerbero fedora x86_64 #13085512
gstreamer

00:04:24

passed build cerbero macos x86_64 #13085516
gst-macos-11.1

00:15:46

passed build clang fedora x86_64 #13085508

00:03:14

manual build msys2 #13085511
docker windows 1809 allowed to fail manual
passed build nodebug fedora x86_64 #13085505

00:04:52

passed build static fedora x86_64 #13085506

00:03:21

passed build static nodebug fedora x86_64 #13085507

00:04:51

passed build vs2017 amd64 #13085509
docker windows 1809

00:09:03

passed build vs2017 x86 #13085510
docker windows 1809

00:09:18

 
  Test
passed check fedora #13085518
gstreamer

00:06:41

passed integration testsuites fedora 1/4 #13085519
gstreamer

00:07:49

passed integration testsuites fedora 2/4 #13085520
gstreamer

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passed integration testsuites fedora 3/4 #13085521
gstreamer

00:07:21

passed integration testsuites fedora 4/4 #13085522
gstreamer

00:06:51

passed valgrind bad #13085523
gstreamer

00:06:15

 
  Integrate
passed cross-android universal examples #13085524

00:06:25

passed cross-ios universal examples #13085526
gst-ios-14.3

00:04:14

passed documentation #13085525

00:12:40