gitk: remove header of now empty section "General options"

An earlier commit remove the only option that was available under
"General options". We don't need the header for the empty section.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>

gitk

@@ -11707,8 +11707,6 @@ proc prefspage_general {notebook} {
     pack configure $page.webbrowserf.l -padx 10
     grid x $page.webbrowserf $page.webbrowser -sticky ew
 
-    ttk::label $page.lgen -text [mc "General options"] -font mainfontbold
-    grid $page.lgen - -sticky w -pady 10
     return $page
 }