Revert "thunderbird: set build timeout at eight hours"

The default timeout is 10h on Hydra currently, so this timeout
setting is pointless or counterproductive.
This commit seems to have been made in error
#96767 (comment)

This reverts commit 1733d51.

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

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