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/paymentserver.cpp

@@ -41,12 +41,7 @@
 #include <QSslSocket>
 #include <QStringList>
 #include <QTextDocument>
-
-#if QT_VERSION < 0x050000
-#include <QUrl>
-#else
 #include <QUrlQuery>
-#endif
 
 const int BITCOIN_IPC_CONNECT_TIMEOUT = 1000; // milliseconds
 const QString BITCOIN_IPC_PREFIX("bitcoin:");
@@ -100,11 +95,7 @@ static QList<QString> savedPaymentRequests;
 
 static void ReportInvalidCertificate(const QSslCertificate& cert)
 {
-#if QT_VERSION < 0x050000
-    qDebug() << QString("%1: Payment server found an invalid certificate: ").arg(__func__) << cert.serialNumber() << cert.subjectInfo(QSslCertificate::CommonName) << cert.subjectInfo(QSslCertificate::OrganizationalUnitName);
-#else
     qDebug() << QString("%1: Payment server found an invalid certificate: ").arg(__func__) << cert.serialNumber() << cert.subjectInfo(QSslCertificate::CommonName) << cert.subjectInfo(QSslCertificate::DistinguishedNameQualifier) << cert.subjectInfo(QSslCertificate::OrganizationalUnitName);
-#endif
 }
 
 //
@@ -157,13 +148,11 @@ void PaymentServer::LoadRootCAs(X509_STORE* _store)
             continue;
         }
 
-#if QT_VERSION >= 0x050000
         // Blacklisted certificate
         if (cert.isBlacklisted()) {
             ReportInvalidCertificate(cert);
             continue;
         }
-#endif
         QByteArray certData = cert.toDer();
         const unsigned char *data = (const unsigned char *)certData.data();
 
@@ -413,11 +402,7 @@ void PaymentServer::handleURIOrFile(const QString& s)
     }
     else if (s.startsWith(BITCOIN_IPC_PREFIX, Qt::CaseInsensitive)) // bitcoin: URI
     {
-#if QT_VERSION < 0x050000
-        QUrl uri(s);
-#else
         QUrlQuery uri((QUrl(s)));
-#endif
         if (uri.hasQueryItem("r")) // payment request URI
         {
             QByteArray temp;