Redundant forward declaration

Source commit: 0a2a7b6cd26759fd62aa4c4bd7ff280bb286f7fd

source/filezilla/FtpControlSocket.h

@@ -11,7 +11,6 @@ class CTransferSocket;
 class CMainThread;
 //---------------------------------------------------------------------------
 class CAsyncProxySocketLayer;
-class CMainThread;
 //---------------------------------------------------------------------------
 #define CSMODE_NONE             0x0000
 #define CSMODE_CONNECT          0x0001