Remove redundant overload and simplify comparison

Other places in the code call IsFavourite with other types of objects
that aren't strings (like a GitBranch instance). We either have overloads
for all of them or we just take a string and the caller should know
what to pass us, less of an API footprint to worry about.

Author: shana

src/UnityExtension/Assets/Editor/GitHub.Unity/UI/BranchesView.cs

@@ -309,19 +309,9 @@ private int CompareBranches(GitBranch a, GitBranch b)
             return 0;
         }
 
-        private bool IsFavourite(BranchTreeNode branch)
-        {
-            return IsFavourite(branch.Name);
-        }
-
         private bool IsFavourite(string branchName)
         {
-            if (string.IsNullOrEmpty(branchName))
-            {
-                return false;
-            }
-
-            return favouritesList.Contains(branchName);
+            return !String.IsNullOrEmpty(branchName) && favouritesList.Contains(branchName);
         }
 
         private void OnLocalBranchesUpdate(IEnumerable<GitBranch> list)
@@ -636,7 +626,7 @@ private void OnTreeNodeGUI(BranchTreeNode node)
 
                 if (node.Type != NodeType.Folder)
                 {
-                    var favourite = IsFavourite(node);
+                    var favourite = IsFavourite(node.Name);
                     if (Event.current.type == EventType.Repaint)
                     {
                         GUI.DrawTexture(favouriteRect, favourite ? Styles.FavouriteIconOn : Styles.FavouriteIconOff);