Remove an unnecessary allocation from RestoreBuilder.ToReferenceItems

The nested ToReferenceItem method was creating an ImmutableArray, but not using it. Went ahead and removed that line, and then since that method was only a single line, just pushed it's remaining contents to the caller.

There was a surprising amount of allocations going on in this line, which I happened to find while looking at the solution load section of a speedometer trace. Overall, this was about 0.3% of allocations in this profile.

src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/PackageRestore/Snapshots/RestoreBuilder.cs

@@ -50,14 +50,7 @@ public static ProjectRestoreInfo ToProjectRestoreInfo(IImmutableDictionary<strin
 
             static ImmutableArray<ReferenceItem> ToReferenceItems(IImmutableDictionary<string, IImmutableDictionary<string, string>> items)
             {
-                return items.ToImmutableArray(static (key, value) => ToReferenceItem(key, value));
-
-                static ReferenceItem ToReferenceItem(string name, IImmutableDictionary<string, string> metadata)
-                {
-                    var properties = metadata.ToImmutableArray(static (key, value) => new ReferenceProperty(key, value));
-
-                    return new ReferenceItem(name, metadata);
-                }
+                return items.ToImmutableArray(static (name, metadata) => new ReferenceItem(name, metadata));
             }
         }
     }