Drop unused variables and lambda captures

Also, add context to connect() expressions where we are or were
capturing "this".

Change-Id: I6e006ba6f83d532478018550d148ee93eca59605
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/breakhandler.cpp

@@ -2012,7 +2012,7 @@ bool BreakHandler::contextMenuEvent(const ItemViewEvent &ev)
 
     addAction(menu, tr("Synchronize Breakpoints"),
               Internal::hasSnapshots(),
-              [this] { Internal::synchronizeBreakpoints(); });
+              [] { Internal::synchronizeBreakpoints(); });
 
     menu->addSeparator();
     menu->addAction(action(UseToolTipsInBreakpointsView));