Clean up migrateColor utility

ts/util/migrateColor.ts

@@ -1,51 +1,22 @@
-// Copyright 2018-2020 Signal Messenger, LLC
+// Copyright 2018-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import { ColorType } from '../types/Colors';
 
-type OldColorType =
-  | 'amber'
-  | 'blue'
-  | 'blue_grey'
-  | 'brown'
-  | 'cyan'
-  | 'deep_orange'
-  | 'deep_purple'
-  | 'green'
-  | 'grey'
-  | 'indigo'
-  | 'lime'
-  | 'light_blue'
-  | 'light_green'
-  | 'orange'
-  | 'pink'
-  | 'purple'
-  | 'red'
-  | 'teal'
-  | 'yellow'
-  | 'ultramarine'
-  | string
-  | undefined;
-
-export function migrateColor(color?: OldColorType): ColorType {
+export function migrateColor(color?: string): ColorType {
   switch (color) {
     // These colors no longer exist
     case 'orange':
     case 'amber':
       return 'deep_orange';
-
     case 'yellow':
       return 'brown';
-
     case 'deep_purple':
       return 'purple';
-
     case 'light_blue':
       return 'blue';
-
     case 'cyan':
       return 'teal';
-
     case 'lime':
       return 'light_green';