gui: Remove QT_VERSION fallbacks for Qt < 5

There were surprisingly many `#ifdef` fallbacks for Qt 4.

Remiving them simplifies maintenance, as well as adding new GUI
functionality.

src/qt/sendcoinsentry.cpp

@@ -32,9 +32,7 @@ SendCoinsEntry::SendCoinsEntry(const PlatformStyle *_platformStyle, QWidget *par
 
     if (platformStyle->getUseExtraSpacing())
         ui->payToLayout->setSpacing(4);
-#if QT_VERSION >= 0x040700
     ui->addAsLabel->setPlaceholderText(tr("Enter a label for this address to add it to your address book"));
-#endif
 
     // normal bitcoin address field
     GUIUtil::setupAddressWidget(ui->payTo, this);