tooltip: Don't play games with max-width-chars

Setting max-width-chars to the number of characters
in the string works ok only as long as the average
char width we get from Pango matches reality. Sadly
that seems not always the case, and this code was
causing short Chinese tooltips to always be broken
into two lines.

Fixes: #4470

gtk/gtktooltipwindow.c

@@ -413,11 +413,7 @@ update_label_width (GtkLabel *label)
     }
   else
     {
-      int len;
-
-      len = g_utf8_strlen (text, -1);
-
-      gtk_label_set_max_width_chars (label, MIN (len, 50));
+      gtk_label_set_max_width_chars (label, 50);
       gtk_label_set_wrap (label, TRUE);
     }
 }