refactor: remove <util/system.h> include from wallet.h

Since we no longer store a ref to the global `ArgsManager`
inside the wallet, we can move the util/system.h
include to the cpp.

This dependency removal opened a can of worms, as few
other places were, invalidly, depending on the wallet's
header including it.

src/qt/optionsmodel.cpp

@@ -18,6 +18,7 @@
 #include <netbase.h>
 #include <txdb.h>       // for -dbcache defaults
 #include <util/string.h>
+#include <util/system.h>
 #include <validation.h> // For DEFAULT_SCRIPTCHECK_THREADS
 #include <wallet/wallet.h> // For DEFAULT_SPEND_ZEROCONF_CHANGE
 
@@ -640,6 +641,11 @@ bool OptionsModel::isRestartRequired() const
     return settings.value("fRestartRequired", false).toBool();
 }
 
+bool OptionsModel::hasSigner()
+{
+    return gArgs.GetArg("-signer", "") != "";
+}
+
 void OptionsModel::checkAndMigrate()
 {
     // Migration of default values

src/qt/optionsmodel.h

@@ -98,6 +98,9 @@ public:
     bool getEnablePSBTControls() const { return m_enable_psbt_controls; }
     const QString& getOverriddenByCommandLine() { return strOverriddenByCommandLine; }
 
+    /** Whether -signer was set or not */
+    bool hasSigner();
+
     /* Explicit setters */
     void SetPruneTargetGB(int prune_target_gb);
 

src/qt/sendcoinsdialog.cpp

@@ -203,7 +203,7 @@ void SendCoinsDialog::setModel(WalletModel *_model)
         if (model->wallet().hasExternalSigner()) {
             //: "device" usually means a hardware wallet.
             ui->sendButton->setText(tr("Sign on device"));
-            if (gArgs.GetArg("-signer", "") != "") {
+            if (model->getOptionsModel()->hasSigner()) {
                 ui->sendButton->setEnabled(true);
                 ui->sendButton->setToolTip(tr("Connect your hardware wallet first."));
             } else {

src/wallet/dump.cpp

@@ -5,6 +5,7 @@
 #include <wallet/dump.h>
 
 #include <fs.h>
+#include <util/system.h>
 #include <util/translation.h>
 #include <wallet/wallet.h>
 

src/wallet/rpc/util.cpp

@@ -6,6 +6,7 @@
 
 #include <common/url.h>
 #include <rpc/util.h>
+#include <util/system.h>
 #include <util/translation.h>
 #include <wallet/context.h>
 #include <wallet/wallet.h>

src/wallet/wallet.cpp

@@ -34,6 +34,7 @@
 #include <util/moneystr.h>
 #include <util/rbf.h>
 #include <util/string.h>
+#include <util/system.h>
 #include <util/translation.h>
 #include <wallet/coincontrol.h>
 #include <wallet/context.h>

src/wallet/wallet.h

@@ -10,6 +10,7 @@
 #include <fs.h>
 #include <interfaces/chain.h>
 #include <interfaces/handler.h>
+#include <logging.h>
 #include <outputtype.h>
 #include <policy/feerate.h>
 #include <psbt.h>
@@ -19,7 +20,6 @@
 #include <util/result.h>
 #include <util/strencodings.h>
 #include <util/string.h>
-#include <util/system.h>
 #include <util/time.h>
 #include <util/ui_change_type.h>
 #include <validationinterface.h>