Merge #12764: doc: Remove field in getblocktemplate help that has never been used.

ac8a1d092e [RPC] Remove field in getblocktemplate help that has never been used (Conor Scott)

Pull request description:

  [BIP 22 - getblocktemplate](https://github.com/bitcoin/bips/blob/master/bip-0022.mediawiki#Transactions%20Object%20Format) specifies an optional flag, `required` if the transaction must be in the block.

  Luke's implementation #936 did not include this flag, and it was later added to the help description in #3246 (more than a year later) but the field was still never actually implemented. As far as I can tell, bitcoin core would have never actually included this in a `getblocktemplate` call, so it seems logical to remove it from the help description.

  If I am missing something or this is considered harmless - I can close the PR.

Tree-SHA512: f25dda51cc4e1512aff69309be04e3053bdccc1cf03c8d58e8866aa1fdf9d86cc57df872e85528351fc8a8d6d64a8f46a36c513680834762d854f368fbeb0f44

src/rpc/mining.cpp

@@ -337,7 +337,6 @@ static UniValue getblocktemplate(const JSONRPCRequest& request)
             "         \"fee\": n,                    (numeric) difference in value between transaction inputs and outputs (in satoshis); for coinbase transactions, this is a negative Number of the total collected block fees (ie, not including the block subsidy); if key is not present, fee is unknown and clients MUST NOT assume there isn't one\n"
             "         \"sigops\" : n,                (numeric) total SigOps cost, as counted for purposes of block limits; if key is not present, sigop cost is unknown and clients MUST NOT assume it is zero\n"
             "         \"weight\" : n,                (numeric) total transaction weight, as counted for purposes of block limits\n"
-            "         \"required\" : true|false      (boolean) if provided and true, this transaction must be in the final block\n"
             "      }\n"
             "      ,...\n"
             "  ],\n"