message: fix: remove duplicate Subscribable<T> interface declaration
  also remove unused import in types.ts
diff: import { Observable } from './Observable';
  -import { Action as _Action } from './scheduler/Action';
  import { Subscription } from './Subscription';
  /** OPERATOR INTERFACES */
  @@ -35,12 +34,6 @@ export interface SubscriptionLike extends Unsubscribable {
  readonly closed: boolean;
  }
  -export interface Subscribable<T> {
  - subscribe(observerOrNext?: PartialObserver<T> | ((value: T) => void),
  - error?: (error: any) => void,
  - complete?: () => void): Unsubscribable;
  -}
  -
  export type SubscribableOrPromise<T> = Subscribable<T> | Subscribable<never> | PromiseLike<T> | ObservableLike<T>;
  /** OBSERVABLE INTERFACES */
  