message: refactor(forms): remove unused internal function
  The `isFormControlOptions` function is never used, and can be safely removed as it is not a public API.
  PR Close
diff: * found in the LICENSE file at https://angular.io/license
  */
  -import {inject, Injectable, InjectionToken} from '@angular/core';
  +import {inject, Injectable} from '@angular/core';
  import {AsyncValidatorFn, ValidatorFn} from './directives/validators';
  import {ReactiveFormsModule} from './form_providers';
  @@ -23,14 +23,6 @@ function isAbstractControlOptions(options: AbstractControlOptions|{[key: string]
  (options as AbstractControlOptions).updateOn !== undefined);
  }
  -function isFormControlOptions(options: FormControlOptions|{[key: string]: any}|null|
  - undefined): options is FormControlOptions {
  - return !!options &&
  - (isAbstractControlOptions(options) ||
  - (options as FormControlOptions).initialValueIsDefault !== undefined ||
  - (options as FormControlOptions).nonNullable !== undefined);
  -}
  -
  /**
  * ControlConfig<T> is a tuple containing a value of type T, plus optional validators and async
  * validators.
  