Remove unused code to create terminals with custom titles

Irrespective of how you create a new terminal (over D-Bus using
$bindir/gnome-terminal, ctrl+shift n, or the application menu), the
code to set a custom title during construction was unused. Possibly
as a result of f27bf0135a2d18ba22158d28bf1f8c5f6ec066c8

https://bugzilla.gnome.org/show_bug.cgi?id=724110