rpc: remove scantxoutset EXPERIMENTAL warning

Summary:
Also remove an unnecessary leading "\n" (see D7184)

This is a backport of [[bitcoin/bitcoin#21426 | core#21426]]

Test Plan: `src/bitcoin-cli help scantxoutset`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11338

src/rpc/blockchain.cpp

@@ -2645,9 +2645,7 @@ static RPCHelpMan scantxoutset() {
     const auto &ticker = Currency::get().ticker;
     return RPCHelpMan{
         "scantxoutset",
-        "EXPERIMENTAL warning: this call may be removed or changed in future "
-        "releases.\n"
-        "\nScans the unspent transaction output set for entries that match "
+        "Scans the unspent transaction output set for entries that match "
         "certain output descriptors.\n"
         "Examples of output descriptors are:\n"
         "    addr(<address>)                      Outputs whose scriptPubKey "