Move spawnSwitchErr to @0xproject/utils

packages/website/ts/utils/utils.ts

@@ -33,9 +33,6 @@ export const utils = {
             throw new Error(message);
         }
     },
-    spawnSwitchErr(name: string, value: any): Error {
-        return new Error(`Unexpected switch value: ${value} encountered for ${name}`);
-    },
     isNumeric(n: string): boolean {
         return !isNaN(parseFloat(n)) && isFinite(Number(n));
     },