git-gui: always use themed widgets from ttk

git-gui optionally uses themed ui elements from ttk, but the full set of
ttk ui elements is always available with Tk 8.6.  Keeping code making
ttk use optional increases maintenance burden for no benefit.  Let's use
ttk always, allowing removal of alternate code paths in subsequent
patches.

Signed-off-by: Mark Levedahl <[email protected]>

Author: mark987

git-gui.sh

@@ -913,15 +913,11 @@ proc apply_config {} {
 	}
 
 	global use_ttk NS
-	set use_ttk 0
-	set NS {}
-	if {$repo_config(gui.usettk)} {
-		set use_ttk 1
-		set NS ttk
-		bind [winfo class .] <<ThemeChanged>> [list InitTheme]
-		pave_toplevel .
-		color::sync_with_theme
-	}
+	set use_ttk 1
+	set NS ttk
+	bind [winfo class .] <<ThemeChanged>> [list InitTheme]
+	pave_toplevel .
+	color::sync_with_theme
 
 	global comment_string
 	set comment_string [get_config core.commentstring]