Debugger: Inline GdbEngine::write into caller

Not used in earnest since the end of CODA/Symbian.

Change-Id: Ib2d22fb247d178b091a17f9927aa911d6707d3f9
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/gdb/gdbengine.h

@@ -419,9 +419,6 @@ protected:
     void debugLastCommand() override;
     DebuggerCommand m_lastDebuggableCommand;
 
-protected:
-    virtual void write(const QByteArray &data);
-
 protected:
     bool prepareCommand();
     void interruptLocalInferior(qint64 pid);