Merge #14403: qt: Revert "Force TLS1.0+ for SSL connections"

7d173c4cd1 qt: Revert "Force TLS1.0+ for SSL connections" (Tim Ruffing)

Pull request description:

  This reverts commit 15e26a6a9a, whose
  purpose was to tweak the Qt configuration to force TLS, i.e., to
  disable SSLv3, in Qt versions >= 5.5. However, the default behavior
  of Qt >= 5.4 is to disable SSLv3 anyway [1], so the configuration
  tweak is redundant.

  With Qt 5.11.2, the configuration tweak is not only redundant but in
  fact provokes a deadlock due to a bug in Qt 5.11.2. Since the deadlock
  occurs at the early startup stage of bitcoin-qt, it renders bitcoin-qt
  entirely non-functional when compiled against Qt 5.11.2 (and maybe
  other Qt versions).

  Fixes #14359.

  [1] https://code.qt.io/cgit/qt/qtbase.git/commit/?id=3fd2d9eff8c1f948306ee5fbfe364ccded1c4b84

Tree-SHA512: 9dd86557b8d265dfa56592924778a736590f2e6a0b2acf77d4f9f4200206a9edaa79b144b0085ea59ac0cc1bc66d9740402fd02f9298ff74c8d6f526f3f725d6

src/qt/bitcoin.cpp

@@ -51,7 +51,6 @@
 #include <QThread>
 #include <QTimer>
 #include <QTranslator>
-#include <QSslConfiguration>
 
 #if defined(QT_STATICPLUGIN)
 #include <QtPlugin>
@@ -577,13 +576,6 @@ int main(int argc, char *argv[])
 #ifdef Q_OS_MAC
     QApplication::setAttribute(Qt::AA_DontShowIconsInMenus);
 #endif
-#if QT_VERSION >= 0x050500
-    // Because of the POODLE attack it is recommended to disable SSLv3 (https://disablessl3.com/),
-    // so set SSL protocols to TLS1.0+.
-    QSslConfiguration sslconf = QSslConfiguration::defaultConfiguration();
-    sslconf.setProtocol(QSsl::TlsV1_0OrLater);
-    QSslConfiguration::setDefaultConfiguration(sslconf);
-#endif
 
     // Register meta types used for QMetaObject::invokeMethod
     qRegisterMetaType< bool* >();