[PR] Remove shadowed generics in Proxy$traps

Summary:
In v0.67.0, `Proxy$traps.getOwnPropertyDescriptor` and
`Proxy$traps.defineProperty` were erroneously modified with an
additional generic, which shadowed the surrounding generic. By removing
it, these two methods will now correctly refer to the proxy target's
type, instead of an independently inferred type.

MDN docs for `getOwnPropertyDescriptor`:
<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/handler/getOwnPropertyDescriptor>

MDN docs for `defineProperty`:
<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/handler/defineProperty>
Pull Request resolved: #6750

Reviewed By: jbrown215

Differential Revision: D14071096

Pulled By: nmote

fbshipit-source-id: 659756f6ca2d93ab8ef0b2c9813d67a4592a2991

lib/core.js

@@ -799,8 +799,8 @@ type Proxy$traps<T> = {
   setPrototypeOf?: (target: T, prototype: Object|null) => boolean;
   isExtensible?: (target: T) => boolean;
   preventExtensions?: (target: T) => boolean;
-  getOwnPropertyDescriptor?: <T>(target: T, property: string) => void | PropertyDescriptor<T>;
-  defineProperty?: <T>(target: T, property: string, descriptor: PropertyDescriptor<T>) => boolean;
+  getOwnPropertyDescriptor?: (target: T, property: string) => void | PropertyDescriptor<T>;
+  defineProperty?: (target: T, property: string, descriptor: PropertyDescriptor<T>) => boolean;
   has?: (target: T, key: string) => boolean;
   get?: (target: T, property: string, receiver: Proxy<T>) => any;
   set?: (target: T, property: string, value: any, receiver: Proxy<T>) => boolean;