Merge #16708: qt: Replace obsolete functions of QSslSocket

2e1455c Replace obsolete functions of QSslSocket (Hennadii Stepanov)

Pull request description:

  The [`QSslSocket::setDefaultCaCertificates()`](https://doc.qt.io/qt-5/qsslsocket-obsolete.html#setDefaultCaCertificates) and [`QSslSocket::systemCaCertificates()`](https://doc.qt.io/qt-5/qsslsocket-obsolete.html#systemCaCertificates) member functions are [obsolete](https://doc.qt.io/qt-5.12/qsslsocket-obsolete.html) since Qt 5.12.

  This PR replaces them, does not change behavior and keeps compatibility with [Qt 5.5.1](#15393).

ACKs for top commit:
  laanwj:
    ACK 2e1455c
  promag:
    ACK 2e1455c.

Tree-SHA512: 4182cd22a3e7a998d62a0fe84e748803a6962a65920b74da9fcf5666a700507468bb6e428054ccb70c2fbb7969a56933f450bc405c7a32ecbc1f8af4c1f983a3

Author: laanwj

src/qt/paymentserver.cpp

@@ -41,8 +41,8 @@
 #include <QNetworkReply>
 #include <QNetworkRequest>
 #include <QSslCertificate>
+#include <QSslConfiguration>
 #include <QSslError>
-#include <QSslSocket>
 #include <QStringList>
 #include <QTextDocument>
 #include <QUrlQuery>
@@ -448,9 +448,9 @@ void PaymentServer::LoadRootCAs(X509_STORE* _store)
 
         certList = QSslCertificate::fromPath(certFile);
         // Use those certificates when fetching payment requests, too:
-        QSslSocket::setDefaultCaCertificates(certList);
+        QSslConfiguration::defaultConfiguration().setCaCertificates(certList);
     } else
-        certList = QSslSocket::systemCaCertificates();
+        certList = QSslConfiguration::systemCaCertificates();
 
     int nRootCerts = 0;
     const QDateTime currentTime = QDateTime::currentDateTime();