docs: make role of getQuartzComponents more clear and also make it optional

quartz/plugins/emitters/cname.ts

@@ -11,9 +11,6 @@ export function extractDomainFromBaseUrl(baseUrl: string) {
 
 export const CNAME: QuartzEmitterPlugin = () => ({
   name: "CNAME",
-  getQuartzComponents() {
-    return []
-  },
   async getDependencyGraph(_ctx, _content, _resources) {
     return new DepGraph<FilePath>()
   },