Revert "Use builtin libav"

This reverts commit 149bc9efc2.

gstreamer1-libav.spec

@@ -1,5 +1,3 @@
-%global builtin_libav 1
-
 Name:           gstreamer1-libav
 Version:        1.18.2
 Release:        2%{?dist}
@@ -15,7 +13,7 @@ BuildRequires:  gstreamer1-plugins-base-devel >= %{version}
 BuildRequires:  orc-devel
 BuildRequires:  bzip2-devel
 BuildRequires:  zlib-devel
-%{!?builtin_libav:BuildRequires:  ffmpeg-devel}
+BuildRequires:  ffmpeg-devel
 
 %description
 GStreamer is a streaming media framework, based on graphs of filters which