codecs: h264picture: use g_array_remove_index_fast()

This algorithm is faster than the normal one. The problem is it
disorders the elements in the dpb, but it does not seem to mess
decoders.

Part-of: <gstreamer/gst-plugins-bad!1378>
29 jobs for remove_index_fast in 5 minutes and 24 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build Docker
passed #3338965
gstreamer
alpine amd64 manifest builder docker

00:01:26

passed #3338964
gstreamer
android docker

00:03:49

passed #3338963
gstreamer
cerbero fedora amd64 docker

00:04:36

passed #3338962
gstreamer
fedora amd64 docker

00:04:57

passed #3338966
gstreamer
gst-indent amd64 docker

00:01:38

 
  Preparation
passed #3338968
gst indent

00:00:26

manual #3338967
manual
manifest
 
  Build
created #3338977
gstreamer
build cerbero cross-android universal
created #3338984
gst-ios-13.2
build cerbero cross-ios universal
created #3338978
gstreamer
build cerbero cross win32
created #3338980
gstreamer
build cerbero cross win64
created #3338976
gstreamer
build cerbero fedora x86_64
created #3338982
gst-macos-10.15
build cerbero macos x86_64
created #3338972
build clang fedora x86_64
created #3338975
1809 windows docker allowed to fail manual
build msys2
created #3338969
build nodebug fedora x86_64
created #3338970
build static fedora x86_64
created #3338971
build static nodebug fedora x86_64
created #3338973
1809 windows docker
build vs2017 amd64
created #3338974
1809 windows docker
build vs2017 x86
 
  Test
created #3338986
gstreamer
check fedora
created #3338988
gstreamer
integration testsuites fedora 1/4
created #3338991
gstreamer
integration testsuites fedora 2/4
created #3338993
gstreamer
integration testsuites fedora 3/4
created #3338996
gstreamer
integration testsuites fedora 4/4
created #3338998
gstreamer
valgrind bad
 
  Integrate
created #3339000
cross-android universal examples
created #3339003
gst-ios-13.2
cross-ios universal examples
created #3339002
documentation