Unify QLatin1String and QLatin1Literal

Unify QLatin1String and QLatin1Literal

Unify the two classes and get rid of one
TODO item for Qt 5.

Using strlen in the constructor of QLatin1String works,
as the compiler can do the calculation at compile time.

Change-Id: I59d98c71a34b86d4211fa0d8cfd40b7d612c5a78
Reviewed-on: http://codereview.qt.nokia.com/1219
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>