vpx: Fix build against libvpx 1.8

The deprecated debug visualizer was removed.
8 jobs for <span class="ref-name">libvpx-1.8</span> in 15 minutes and 54 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Preparation
passed #101821
gst indent

00:00:15

passed #101820
manifest

00:00:17

 
  Build
passed #101822
build fedora x86_64

00:03:09

 
  Test
passed #101823
check fedora

00:03:17

 
  Full Builds
passed #101824
build android arm64 api28

00:04:06

passed #101826
build cerbero cross win32

00:09:09

passed #101827
build cerbero cross win64

00:07:48

passed #101825
build cerbero fedora x86_64

00:07:53