remnant of env branch rebase

Author: ylafon

org/w3c/css/values/CssEnv.java

@@ -186,7 +186,6 @@ public String toStringEmpty() {
     private boolean _isCheckableType(int type) {
         switch (type) {
             case CssTypes.CSS_ANGLE:
-            case CssTypes.CSS_CLAMP:
             case CssTypes.CSS_FLEX:
             case CssTypes.CSS_FREQUENCY:
             case CssTypes.CSS_LENGTH: