Q(Styled)ItemDelegate: code tidies

Fix a comment and move another out of a ifdef.

Change-Id: Ib1bc2efba34bd37aa8525621e430d7f6094238ae
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
tst_qdatawidgetmapper: stop using module-wide includes

Change-Id: Ia0e170e2185a46685cb1c130a16b8a9d379b6e02
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>