Revert "Merge #102138: thunderbird: set build timeout at eight hours"

This reverts commit ef543fb416353320ba2876754e3d3240d338865e, reversing
changes made to 0d657b9c61d1b568584805717f640b2bbc5a9b0e.
See the parent commit.

pkgs/applications/networking/mailreaders/thunderbird/default.nix

@@ -332,6 +332,5 @@ stdenv.mkDerivation rec {
     ];
     platforms = platforms.linux;
     license = licenses.mpl20;
-    timeout = 28800; # eight hours
   };
 }