Starting to get rid of Q_UNUSED declarations for unused function parameters.

Starting to get rid of Q_UNUSED declarations for unused function parameters.
The official C++ way is to leave out the variable name instead. This has the
advantage to be reliable: In one case a variable declared unused was later
used.

Change-Id: I1c96636f7fa7a621d1594d1e9cacaec75c561faa
Reviewed-on: https://code.wireshark.org/review/9532
Reviewed-by: Jörg Mayer <jmayer@loplof.de>