lodash - change weakmap declaration to work with TS 2.2 (#14662)

* lodash - change weakmap declaration to work with TS 2.2

* remove WeakMap declaration altogether

lodash/index.d.ts

@@ -12701,7 +12701,7 @@ declare namespace _ {
          * @param value The value to check.
          * @returns Returns true if value is correctly classified, else false.
          */
-        isWeakMap<K, V>(value?: any): value is WeakMap<K, V>;
+        isWeakMap<K, V>(value?: any): boolean;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -19446,5 +19446,4 @@ declare global {
     interface Set<T> { }
     interface Map<K, V> { }
     interface WeakSet<T> { }
-    interface WeakMap<K, V> { }
 }

lodash/lodash-tests.ts

@@ -7435,17 +7435,6 @@ namespace TestIsUndefined {
 
 // _.isWeakMap
 namespace TestIsWeakMap {
-    {
-        let value: number|WeakMap<string, number>;
-
-        if (_.isWeakMap<string, number>(value)) {
-            let result: WeakMap<string, number> = value;
-        }
-        else {
-            let result: number = value;
-        }
-    }
-
     {
         let result: boolean;