refactor(docs-infra): fix docs examples for tslint rules related to object properties (#38143)

This commit updates the docs examples to be compatible with the
`no-string-literal`, `object-literal-key-quotes` and
`object-literal-shorthand` tslint rules.

This is in preparation of updating the docs examples `tslint.json` to
match the one generated for new Angular CLI apps in a future commit.

PR Close #38143

aio/content/examples/dynamic-form/src/app/question-dropdown.ts

@@ -3,10 +3,4 @@ import { QuestionBase } from './question-base';
 
 export class DropdownQuestion extends QuestionBase<string> {
   controlType = 'dropdown';
-  options: {key: string, value: string}[] = [];
-
-  constructor(options: {} = {}) {
-    super(options);
-    this.options = options['options'] || [];
-  }
 }