reduceRight is never used (microsoft#19605)

Author: Andy

src/compiler/core.ts

@@ -985,32 +985,6 @@ namespace ts {
         return initial;
     }
 
-    export function reduceRight<T, U>(array: ReadonlyArray<T>, f: (memo: U, value: T, i: number) => U, initial: U, start?: number, count?: number): U;
-    export function reduceRight<T>(array: ReadonlyArray<T>, f: (memo: T, value: T, i: number) => T): T;
-    export function reduceRight<T>(array: T[], f: (memo: T, value: T, i: number) => T, initial?: T, start?: number, count?: number): T {
-        if (array) {
-            const size = array.length;
-            if (size > 0) {
-                let pos = start === undefined || start > size - 1 ? size - 1 : start;
-                const end = count === undefined || pos - count < 0 ? 0 : pos - count;
-                let result: T;
-                if (arguments.length <= 2) {
-                    result = array[pos];
-                    pos--;
-                }
-                else {
-                    result = initial;
-                }
-                while (pos >= end) {
-                    result = f(result, array[pos], pos);
-                    pos--;
-                }
-                return result;
-            }
-        }
-        return initial;
-    }
-
     const hasOwnProperty = Object.prototype.hasOwnProperty;
 
     /**