QmlJS checks: Add confusing +/- check.

Migrated from QtChecker.

Change-Id: I06115152f979f9abfa9cbdf4a3e2e63a51ea7284
Reviewed-on: http://codereview.qt-project.org/5858
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>

src/libs/qmljs/qmljsstaticanalysismessage.cpp

@@ -146,12 +146,8 @@ StaticAnalysisMessages::StaticAnalysisMessages()
            tr("do not use void expressions"));
     newMsg(WarnConfusingPluses, Warning,
            tr("confusing pluses"));
-    newMsg(WarnConfusingPreincrement, Warning,
-           tr("confusing preincrement"));
     newMsg(WarnConfusingMinuses, Warning,
            tr("confusing minuses"));
-    newMsg(WarnConfusingPredecrement, Warning,
-           tr("confusing predecrement"));
     newMsg(HintDeclareVarsInOneLine, Hint,
            tr("declare all function vars on a single line"));
     // unused