Remove stale .main class from tree.less (#362)

.main CSS class has a naming conflict with Moncao editor CSS classes and this is causing  A11y issues with Moncao editor.

This class should no longer be used since we moved to the new tree component in REACT, so I am removing it. From my testing, this is not affecting anything.

If we find any styling issue later, we should fix without adding back this class.

less/tree.less

@@ -1,16 +1,5 @@
 @import "./Common/Constants";
 
-.main {
-    width: 100%;
-    float: left;
-    transition: all .0s ease-in-out;
-    -ms-transition: all 0s ease-in-out;
-    -webkit-transition: all 0s ease-in-out;
-    -moz-transition: all .0s ease-in-out;
-    height: 100%;
-    background-color: white;
-    border-left: 0px solid white;
-}
 
 .resourceTree {
     height: 100%;