rpc: Remove duplicate field in RPCHelpMan for gettransactions #26777

The field 'comment' appears twice in TransactionDescriptionString, incorrectly - this commit removes the instance of the comment field without a description, preserving the one with a description.

On master, the duplicate fields can be be viewed here: https://github.com/bitcoin/bitcoin/blob/master/src/wallet/rpc/transactions.cpp#L419-L423

TransactionDescriptionString is included in RPC calls such as listtransactions which have functional tests.

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ACK https://github.com/bitcoin/bitcoin/pull/26777/commits/090ad51c80fe02a73f8988c1d5b867d2e90ab2f3

It was introduced in #22798 (fa10fbc6658fb8d87118cd550e4de406dca45f23) by @MarcoFalke.

Rendered diff:

$ git diff -U4
diff --git a/gettransaction b/gettransaction
index 0157ebf..e2c3c9f 100644
--- a/gettransaction
+++ b/gettransaction
@@ -28,9 +28,8 @@ Result:
     ...
   ],
   "replaced_by_txid" : "hex",              (string, optional) The txid if this tx was replaced.
   "replaces_txid" : "hex",                 (string, optional) The txid if the tx replaces one.
-  "comment" : "str",                       (string, optional)
   "to" : "str",                            (string, optional) If a comment to is associated with the transaction.
   "time" : xxx,                            (numeric) The transaction time expressed in UNIX epoch time.
   "timereceived" : xxx,                    (numeric) The time received expressed in UNIX epoch time.
   "comment" : "str",                       (string, optional) If a comment is associated with the transaction, only present if not empty.
diff --git a/listsinceblock b/listsinceblock
index 3ed074e..9ad992d 100644
--- a/listsinceblock
+++ b/listsinceblock
@@ -48,9 +48,8 @@ Result:
         ...
       ],
       "replaced_by_txid" : "hex",          (string, optional) The txid if this tx was replaced.
       "replaces_txid" : "hex",             (string, optional) The txid if the tx replaces one.
-      "comment" : "str",                   (string, optional)
       "to" : "str",                        (string, optional) If a comment to is associated with the transaction.
       "time" : xxx,                        (numeric) The transaction time expressed in UNIX epoch time.
       "timereceived" : xxx,                (numeric) The time received expressed in UNIX epoch time.
       "comment" : "str",                   (string, optional) If a comment is associated with the transaction, only present if not empty.
diff --git a/listtransactions b/listtransactions
index 3b4a1dc..15a3a17 100644
--- a/listtransactions
+++ b/listtransactions
@@ -44,9 +44,8 @@ Result:
       ...
     ],
     "replaced_by_txid" : "hex",          (string, optional) The txid if this tx was replaced.
     "replaces_txid" : "hex",             (string, optional) The txid if the tx replaces one.
-    "comment" : "str",                   (string, optional)
     "to" : "str",                        (string, optional) If a comment to is associated with the transaction.
     "time" : xxx,                        (numeric) The transaction time expressed in UNIX epoch time.
     "timereceived" : xxx,                (numeric) The time received expressed in UNIX epoch time.
     "comment" : "str",                   (string, optional) If a comment is associated with the transaction, only present if not empty.