lxqtapplication: Remove message handler
lxqtapplication: Remove message handler

..as it produces (useless) debug.log file. And the file is/was misplaced
in .config dir anyway.

For debugging anyone can redirect stdout/stderr to whereever he/she
wants. For message formatting we should use the QT_MESSAGE_PATTERN
(https://doc.qt.io/qt-5/debug.html#warning-and-debugging-messages).

lxde/liblxqt,lxde/liblxqt