meson: clean up workaround for older meson versions that's no longer needed

Part-of: <!172>
21 jobs for master in 1 minute and 9 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build Docker
passed #3490393
alpine amd64 manifest builder docker

00:00:27

passed #3490392
android docker

00:00:46

passed #3490391
cerbero fedora amd64 docker

00:00:23

passed #3490390
fedora amd64 docker

00:00:47

passed #3490394
gst-indent amd64 docker

00:00:46

 
  Preparation
passed #3490396
gst indent

00:00:21

manual #3490395
manual
manifest
 
  Build
created #3490400
build clang fedora x86_64
created #3490403
docker windows 1809 allowed to fail manual
build msys2
created #3490397
build nodebug fedora x86_64
created #3490398
build static fedora x86_64
created #3490399
build static nodebug fedora x86_64
created #3490401
docker windows 1809
build vs2017 amd64
created #3490402
docker windows 1809
build vs2017 x86
 
  Test
created #3490404
gstreamer
check fedora
created #3490405
gstreamer
integration testsuites fedora 1/4
created #3490406
gstreamer
integration testsuites fedora 2/4
created #3490407
gstreamer
integration testsuites fedora 3/4
created #3490408
gstreamer
integration testsuites fedora 4/4
 
  Integrate
created #3490410
documentation
created #3490409
gstreamer-full