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/cmakeprojectmanager/tealeafreader.cpp

@@ -554,7 +554,7 @@ void TeaLeafReader::processCMakeOutput()
 {
     static QString rest;
     rest = lineSplit(rest, m_cmakeProcess->readAllStandardOutput(),
-                     [this](const QString &s) { MessageManager::write(s); });
+                     [](const QString &s) { MessageManager::write(s); });
 }
 
 void TeaLeafReader::processCMakeError()