qt: Rename SetPrune() to InitializePruneSetting()

This function now resets the prune size and is only called after the
intro sequence.

src/qt/bitcoin.h

@@ -67,8 +67,8 @@ public:
     void parameterSetup();
     /// Create options model
     void createOptionsModel(bool resetSettings);
-    /// Update prune value
-    void SetPrune(bool prune);
+    /// Initialize prune setting
+    void InitializePruneSetting(bool prune);
     /// Create main window
     void createWindow(const NetworkStyle *networkStyle);
     /// Create splash screen