Removed "-*-user-select" checks.

MDN precisely states that "user-select" is not a standard property.
https://developer.mozilla.org/en-US/docs/Web/CSS/user-select
Closes gh-385

Author: c7tincu

src/rules/vendor-prefix.js

@@ -73,11 +73,7 @@ CSSLint.addRule({
                 "-ms-transform-origin" : "transform-origin",
 
                 "-moz-box-sizing" : "box-sizing",
-                "-webkit-box-sizing" : "box-sizing",
-
-                "-moz-user-select" : "user-select",
-                "-khtml-user-select" : "user-select",
-                "-webkit-user-select" : "user-select"
+                "-webkit-box-sizing" : "box-sizing"
             };
 
         //event handler for beginning of rules

tests/rules/vendor-prefix.js

@@ -59,11 +59,9 @@
             Assert.areEqual("Missing standard property 'box-shadow' to go along with '-moz-box-shadow'.", result.messages[0].message);
         },
 
-        "Using -moz-user-select should result in a warning.": function(){
+        "Using -moz-user-select should not result in a warning.": function(){
             var result = CSSLint.verify("h1 {  -moz-user-select:none;  }", { "vendor-prefix": 1 });
-            Assert.areEqual(1, result.messages.length);
-            Assert.areEqual("warning", result.messages[0].type);
-            Assert.areEqual("Missing standard property 'user-select' to go along with '-moz-user-select'.", result.messages[0].message);
+            Assert.areEqual(0, result.messages.length);
         },
 
         "Using @font-face should not result in an error (#90)": function(){