Removing fetchgit --depth and its usage. It does not provide much advantages...

I think it takes the recent N commits into the repository, which says very little,
even for wanting master/HEAD.

svn path=/nixpkgs/trunk/; revision=18277

pkgs/build-support/fetchgit/builder.sh

@@ -2,7 +2,7 @@ source $stdenv/setup
 
 header "exporting $url (rev $rev) into $out"
 
-git clone --depth "$depth" "$url" $out
+git clone "$url" $out
 if test -n "$rev"; then
   cd $out
   git checkout $rev