Replace remaining literals BTC with CURRENCY_UNIT

This replaces one remaining instance of the literal "BTC" string with
the CURRENCY_UNIT constant, as is done in most of the codebase already.

The other remaining instance (which is just part of a log message and thus
not really user-visible) is just removed.

After this change, no instance of literal "BTC" remains anywhere in the
non-Qt and non-test codebase.

Author: domob1812

src/validation.cpp

@@ -974,7 +974,7 @@ bool MemPoolAccept::Finalize(ATMPArgs& args, Workspace& ws)
     // Remove conflicting transactions from the mempool
     for (CTxMemPool::txiter it : allConflicting)
     {
-        LogPrint(BCLog::MEMPOOL, "replacing tx %s with %s for %s BTC additional fees, %d delta bytes\n",
+        LogPrint(BCLog::MEMPOOL, "replacing tx %s with %s for %s additional fees, %d delta bytes\n",
                 it->GetTx().GetHash().ToString(),
                 hash.ToString(),
                 FormatMoney(nModifiedFees - nConflictingFees),

src/wallet/rpcwallet.cpp

@@ -3361,7 +3361,7 @@ static UniValue bumpfee(const JSONRPCRequest& request)
             "                         the dust threshold."},
                             {"fee_rate", RPCArg::Type::NUM, /* default */ "fallback to 'confTarget'", "FeeRate (NOT total fee) to pay, in " + CURRENCY_UNIT + " per kB\n"
             "                         Specify a fee rate instead of relying on the built-in fee estimator.\n"
-            "                         Must be at least 0.0001 BTC per kB higher than the current transaction fee rate.\n"},
+                                     "Must be at least 0.0001 " + CURRENCY_UNIT + " per kB higher than the current transaction fee rate.\n"},
                             {"replaceable", RPCArg::Type::BOOL, /* default */ "true", "Whether the new transaction should still be\n"
             "                         marked bip-125 replaceable. If true, the sequence numbers in the transaction will\n"
             "                         be left unchanged from the original. If false, any input sequence numbers in the\n"