ffmpeg: change default 0.10 -> 2.0

This commit, and the "pinnings" that follow should not cause major issues.
I personally checked (build-only) each and every package that depends
on ffmpeg to find the maximum supported version.
I performed this on stdenv-updates+glibc2.18+x-updates but I don't expect
that to matter.

pkgs/top-level/all-packages.nix

@@ -4152,7 +4152,7 @@ let
     texinfo = texinfo5;
   };
 
-  ffmpeg = ffmpeg_0_10;
+  ffmpeg = ffmpeg_2;
 
   ffms = callPackage ../development/libraries/ffms { };