WeakMap remove `.clear()`?

[kitsonk]

From microsoft/TypeScript#10695, for some reason TSJS-lib-generator is picking up .clear() on WeakMap, though the ChakraCore team indicate it is not exposed to JavaScript land (see microsoft/TypeScript#1539)

[zhengbli]

This issue comes from es2015.collection.d.ts, which is not generated by the tool in this repo, it is hand-written instead. This issue should be fixed in the TS main repo.