util: Replace magics with DEFAULT_PRUNE_TARGET_GB

This commit does not change behavior.

Author: hebasto

src/qt/guiconstants.h

@@ -51,4 +51,7 @@ static const int TOOLTIP_WRAP_THRESHOLD = 80;
 /* One gigabyte (GB) in bytes */
 static constexpr uint64_t GB_BYTES{1000000000};
 
+// Default prune target displayed in GUI.
+static constexpr int DEFAULT_PRUNE_TARGET_GB{2};
+
 #endif // BITCOIN_QT_GUICONSTANTS_H

src/qt/intro.cpp

@@ -135,7 +135,7 @@ Intro::Intro(QWidget *parent, uint64_t blockchain_size, uint64_t chain_state_siz
         ui->prune->setChecked(true);
         ui->prune->setEnabled(false);
     }
-    ui->prune->setText(tr("Discard blocks after verification, except most recent %1 GB (prune)").arg(pruneTarget ? pruneTarget / 1000 : 2));
+    ui->prune->setText(tr("Discard blocks after verification, except most recent %1 GB (prune)").arg(pruneTarget ? pruneTarget / 1000 : DEFAULT_PRUNE_TARGET_GB));
     requiredSpace = m_blockchain_size;
     QString storageRequiresMsg = tr("At least %1 GB of data will be stored in this directory, and it will grow over time.");
     if (pruneTarget) {

src/qt/optionsmodel.cpp

@@ -91,7 +91,7 @@ void OptionsModel::Init(bool resetSettings)
     if (!settings.contains("bPrune"))
         settings.setValue("bPrune", false);
     if (!settings.contains("nPruneSize"))
-        settings.setValue("nPruneSize", 2);
+        settings.setValue("nPruneSize", DEFAULT_PRUNE_TARGET_GB);
     SetPrune(settings.value("bPrune").toBool());
 
     if (!settings.contains("nDatabaseCache"))