message: refactor: Remove some unused imports.
diff: import { ObservableInput, OperatorFunction, ObservedValueOf } from '../types';
  -import { map } from './map';
  -import { innerFrom } from '../observable/innerFrom';
  import { operate } from '../util/lift';
  import { mergeInternals } from './mergeInternals';
  -import { isFunction } from '../util/isFunction';
  /**
  * Projects each source value to an Observable which is merged in the output
  