Duplicate global variables declarations in lib/lib.dom.d.ts

[mrbar42]

Some of the global variables are declared twice in lib/lib.dom.d.ts.
While this doesn't cause a direct error, it does cause some issues for obscure uses of this lib.
Nonetheless, assuming there is's no reason for this duplication, it would increase the correctness of the code and there for it is purposed.

The fouling declarations:

declare var caches: CacheStorage;
declare var crypto: Crypto;
declare var indexedDB: IDBFactory;
declare var performance: Performance;
declare var sessionStorage: Storage;
declare var localStorage: Storage;