Change remaining uses of {to,from}Ascii to {to,from}Latin1 [QtCore]

Change remaining uses of {to,from}Ascii to {to,from}Latin1 [QtCore]

This operation should be a no-op anyway, since at this point in time,
the fromAscii and toAscii functions simply call their fromLatin1 and
toLatin1 counterparts.

Task-number: QTBUG-21872
Change-Id: I38f97ad379deafebef02c75d611343ca15640c8a
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@nokia.com>