Less_Tree_Selector: Remove unused _css class property

Usage removed in 38f66ac

Change-Id: I5e580ee10bfb2e26e8430863b8d470f581f14869

Author: umherirrender

.phan/stubs/Less_Tree_Selector.php

@@ -6,7 +6,6 @@ class Less_Tree_Selector extends Less_Tree {
 	public $elements;
 	public $condition;
 	public $extendList = [];
-	public $_css;
 	public $index;
 	public $evaldCondition = false;
 	public $currentFileInfo = [];

lib/Less/Tree/Selector.php

@@ -7,7 +7,6 @@ class Less_Tree_Selector extends Less_Tree {
 	public $elements;
 	public $condition;
 	public $extendList = [];
-	public $_css;
 	public $index;
 	public $evaldCondition = false;
 	public $currentFileInfo = [];