Merge #15833: [doc] remove out-of-date comment on pay-to-witness support

2d8ba4f remove out-of-date comment on pay-to-witness support (r8921039)

Pull request description:

  The comment below on function 'ExtractDestinations' was added 2017-08-15 while the support was added later on 2017-08-25 through function 'ExtractDestination'.

  ```
  Currently does not extract address from pay-to-witness scripts
  ```

ACKs for commit 2d8ba4:

Tree-SHA512: ce8eb9660c56a8998cc94c8cbc5d47f875045b4aa558f2325cb125ec77794a100f7b73ead12a48a7630aa80483237bb67eb8ee6b0f9a527275ed546718b7a0e1

Author: laanwj

src/script/standard.h

@@ -153,8 +153,7 @@ bool ExtractDestination(const CScript& scriptPubKey, CTxDestination& addressRet)
  * multisig scripts, this populates the addressRet vector with the pubkey IDs
  * and nRequiredRet with the n required to spend. For other destinations,
  * addressRet is populated with a single value and nRequiredRet is set to 1.
- * Returns true if successful. Currently does not extract address from
- * pay-to-witness scripts.
+ * Returns true if successful.
  *
  * Note: this function confuses destinations (a subset of CScripts that are
  * encodable as an address) with key identifiers (of keys involved in a