keypool: Remove superfluous topup from CWallet::GetNewChangeDestination

This does not change behavior. This TopUp() is unnecessary as currently
m_spk_man calls TopUp further down the call stack inside
LegacyScriptPubKeyMan::ReserveKeyFromKeyPool (called by LegacyScriptPubKeyMan::GetReservedDestination)

By removing this here, we also prepare for future changes where CWallet
has multiple ScriptPubKeyMans instead of m_spk_man.

src/wallet/wallet.cpp

@@ -3122,8 +3122,6 @@ bool CWallet::GetNewChangeDestination(const OutputType type, CTxDestination& des
 {
     error.clear();
 
-    m_spk_man->TopUp();
-
     ReserveDestination reservedest(this, type);
     if (!reservedest.GetReservedDestination(dest, true)) {
         error = "Error: Keypool ran out, please call keypoolrefill first";