fix: use GDK_SELECTION_PRIMARY instead of GDK_SELECTION_CLIPBOARD for dictionary lookup on double-click

When double-clicking a word to look it up in the dictionary, Xiphos was
reading GDK_SELECTION_CLIPBOARD, which is filled asynchronously by the
WebKit COPY command. This caused a timing issue where the previous word
was looked up instead of the newly selected one.

The fix reads GDK_SELECTION_PRIMARY instead, which X11 fills
automatically and synchronously when the user double-clicks a word,
making it immediately available for the dictionary lookup.

The now-redundant WebKit COPY block (#ifdef USE_WEBKIT2 ... #endif) has
also been removed as it is no longer needed for this functionality.

Fixes #1212

Author: lafricain79

src/webkit/wk-html.c

@@ -67,15 +67,7 @@ static gboolean button_release_handler(GtkWidget *widget, GdkEventButton *event)
 	if (event->type == GDK_BUTTON_RELEASE && db_click) {
 		XI_message((" button 1 = %s", "double click!\n"));
 
-#ifdef USE_WEBKIT2
-		webkit_web_view_execute_editing_command(WEBKIT_WEB_VIEW(widget),
-							WEBKIT_EDITING_COMMAND_COPY);
-#else
-		if (webkit_web_view_has_selection(WEBKIT_WEB_VIEW(widget))) {
-			webkit_web_view_copy_clipboard(WEBKIT_WEB_VIEW(widget));
-		}
-#endif
-		GtkClipboard *clipboard = gtk_widget_get_clipboard(widget, GDK_SELECTION_CLIPBOARD);
+		GtkClipboard *clipboard = gtk_widget_get_clipboard(widget, GDK_SELECTION_PRIMARY);
 		gtk_clipboard_request_text(clipboard, gui_get_clipboard_text_for_lookup, NULL);
 	}