policy: uncap datacarrier by default

Datacarrier output script sizes and output counts are now
uncapped by default.

To avoid introducing another startup argument, we modify the
OP_RETURN accounting to "budget" the spk sizes.

If a user has set a custom default, this results in that
budget being spent over the sum of all OP_RETURN outputs'
scripts in the transaction, no longer capping the number
of OP_RETURN outputs themselves. This should allow a
superset of current behavior while respecting the passed
argument in terms of total arbitrary data storage.

Co-authored-by: Anthony Towns <aj@erisian.com.au>

test/functional/mempool_accept.py

@@ -326,13 +326,6 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
             result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': 'dust'}],
             rawtxs=[tx.serialize().hex()],
         )
-        tx = tx_from_hex(raw_tx_reference)
-        tx.vout[0].scriptPubKey = CScript([OP_RETURN, b'\xff'])
-        tx.vout = [tx.vout[0]] * 2
-        self.check_mempool_result(
-            result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': 'multi-op-return'}],
-            rawtxs=[tx.serialize().hex()],
-        )
 
         self.log.info('A timelocked transaction')
         tx = tx_from_hex(raw_tx_reference)