Merge bitcoin/bitcoin#30556: doc: multisig-tutorial: remove obsolete mention and link to closed PR

3cd24aa doc: remove obsolete mention and link to closed PR (Marnix)

Pull request description:

  Remove the mention and link as the PR (bitcoin/bitcoin#22341) is closed and the description is wrong/outdated anyway.

ACKs for top commit:
  BrandonOdiwuor:
    ACK 3cd24aa
  tdb3:
    ACK 3cd24aa

Tree-SHA512: 5cd97029337f0cdfe81b6be9401adc4fe51ae2868f8fcadcb03828531a38380a587c32840850a924b6428f62df7d20a1e16ef7414d4078e7bb2c4e359b1fae40

Author: fanquake

doc/multisig-tutorial.md

@@ -16,8 +16,6 @@ This tutorial also uses the default WPKH derivation path to get the xpubs and do
 
 At the time of writing, there is no way to extract a specific path from wallets in Bitcoin Core. For this, an external signer/xpub can be used.
 
-[PR #22341](https://github.com/bitcoin/bitcoin/pull/22341), which is still under development, introduces a new wallet RPC `getxpub`. It takes a BIP32 path as an argument and returns the xpub, along with the master key fingerprint.
-
 ## 1.1 Basic Multisig Workflow
 
 ### 1.1 Create the Descriptor Wallets