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/transactionview.cpp

@@ -95,15 +95,11 @@ TransactionView::TransactionView(const PlatformStyle *platformStyle, QWidget *pa
     hlayout->addWidget(typeWidget);
 
     search_widget = new QLineEdit(this);
-#if QT_VERSION >= 0x040700
     search_widget->setPlaceholderText(tr("Enter address, transaction id, or label to search"));
-#endif
     hlayout->addWidget(search_widget);
 
     amountWidget = new QLineEdit(this);
-#if QT_VERSION >= 0x040700
     amountWidget->setPlaceholderText(tr("Min amount"));
-#endif
     if (platformStyle->getUseExtraSpacing()) {
         amountWidget->setFixedWidth(97);
     } else {