Remove Colors.xml

This wasn't actually doing anything, since all the resource keys we used
came through CodeAnalysisColors's members.

Author: jasonmalinowski

src/EditorFeatures/Core.Wpf/InlineRename/Dashboard/Colors.xaml

@@ -25,10 +25,6 @@
 
     <UserControl.Resources>
         <ResourceDictionary>
-            <ResourceDictionary.MergedDictionaries>
-                <ResourceDictionary Source="Colors.xaml"/>
-            </ResourceDictionary.MergedDictionaries>
-
             <BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
 
             <SolidColorBrush x:Key="ForegroundText" Color="{DynamicResource {x:Static utilities:CodeAnalysisColors.SystemCaptionTextColorKey}}"/>