fdk-aac: change license to fraunhofer-fdk

This library was originally mislicensed as Apache 2.0, as that's the
license used by the project that has this library.

However the library still has the original license on it, so i'm fairly
certain that's the wrong license.

pkgs/development/libraries/fdk-aac/default.nix

···
   meta = with lib; {
     description = "A high-quality implementation of the AAC codec from Android";
     homepage = "https://sourceforge.net/projects/opencore-amr/";
-    license = licenses.asl20;
+    license = licenses.fraunhofer-fdk;
     maintainers = with maintainers; [ codyopel ];
     platforms = platforms.all;
   };