fix(Observable): remove redundant reduce overload

The first overload signature for `reduce` is redundant, since it is simply a special case of the `reduce<T, R>` overload. Its presence breaks type inference when the type of the source observable items and the accumulator differ.

src/operator/reduce.ts

@@ -3,7 +3,6 @@ import { Operator } from '../Operator';
 import { Subscriber } from '../Subscriber';
 
 /* tslint:disable:max-line-length */
-export function reduce<T>(this: Observable<T>, accumulator: (acc: T, value: T, index: number) => T, seed?: T): Observable<T>;
 export function reduce<T>(this: Observable<T>, accumulator: (acc: T[], value: T, index: number) => T[], seed?: T[]): Observable<T[]>;
 export function reduce<T, R>(this: Observable<T>, accumulator: (acc: R, value: T, index: number) => R, seed?: R): Observable<R>;
 /* tslint:enable:max-line-length */