QSslSocket::flush - purge the function marked for removal in Qt6

QAbstractSocket::flush stopped being virtual and, instead, QAbstractSocketPrivate::flush
is now virtual. So the code in QSslSocket is essentially a duplicate.

Change-Id: Iebb33c8490268270b90a662ab64b1ae47c4cbac7
Reviewed-by: Alex Trotsenko <alex1973tr@gmail.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/network/ssl/qsslsocket.cpp

@@ -920,25 +920,6 @@ bool QSslSocket::atEnd() const
     return QAbstractSocket::atEnd();
 }
 
-/*!
-    This function writes as much as possible from the internal write buffer to
-    the underlying network socket, without blocking. If any data was written,
-    this function returns \c true; otherwise false is returned.
-
-    Call this function if you need QSslSocket to start sending buffered data
-    immediately. The number of bytes successfully written depends on the
-    operating system. In most cases, you do not need to call this function,
-    because QAbstractSocket will start sending data automatically once control
-    goes back to the event loop. In the absence of an event loop, call
-    waitForBytesWritten() instead.
-
-    \sa write(), waitForBytesWritten()
-*/
-bool QSslSocket::flush()
-{
-    return d_func()->flush();
-}
-
 /*!
     \since 4.4
 

src/network/ssl/qsslsocket.h

@@ -118,7 +118,6 @@ public:
     bool canReadLine() const override;
     void close() override;
     bool atEnd() const override;
-    bool flush(); // ### Qt6: remove me (implementation moved to private flush())
     void abort();
 
     // From QAbstractSocket: