Use old-style SIGNAL and SLOT macros in tst_qwebsocket.cpp

Without that, this test is failing on some architectures.

Task-number: QTBUG-43804
Done-with: Helge Deller <deller@gmx.de>
Change-Id: I7d275ca6d0baa70e504bbb4a31c65c2ed65d2118
Reviewed-by: Helge Deller <deller@gmx.de>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
Reviewed-by: Lisandro Damián Nicanor Pérez Meyer <perezmeyer@gmail.com>