Usability fix:

Blender's data link button (typically with menu and searching options)
now has a X icon to clear its contents. 

Before you had to click, delete text, enter.

For example:
- Object Parent
- Modifier objects or vertexgroups

This fix saves each user 100 clicks per day, with 100k users
that's 3 billion clicks per year!

source/blender/editors/interface/interface_regions.c

@@ -466,7 +466,7 @@ ARegion *ui_tooltip_create(bContext *C, ARegion *butregion, uiBut *but)
 		data->totline++;
 	}
 
-	if (ELEM3(but->type, TEX, IDPOIN, SEARCH_MENU)) {
+	if (ELEM4(but->type, TEX, IDPOIN, SEARCH_MENU, SEARCH_MENU_UNLINK)) {
 		/* full string */
 		ui_get_but_string(but, buf, sizeof(buf));
 		if (buf[0]) {