gtk+: Remove --disable-debug; This is not a recommended setting.

From http://developer.gnome.org/gtk/2.24/gtk-building.html:

--enable-debug. The default is minimum. Note that no is fast, but
dangerous as it tends to destabilize even mostly bug-free software by
changing the effect of many bugs from simple warnings into fatal
crashes. Thus --enable-debug=no should not be used for stable releases
of GTK+.

Closes Homebrew/homebrew#14874.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/gtk+.rb

@@ -23,8 +23,7 @@ class Gtkx < Formula
   end
 
   def install
-    system "./configure", "--disable-debug",
-                          "--disable-dependency-tracking",
+    system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}",
                           "--disable-glibtest",
                           "--disable-introspection",