Don't remove milliseconds now that toString() includes them.

This patch fixes a test failure introduced by
15da0a5af20fe6771bcb94ef8d46edbd5c8fb64c.

tst_QJSEngine::dateConversionJSQt and tst_QJSEngine::dateConversionQtJS
removed milliseconds from the JS-converted datetime, as
QTime::toString() previously did not include them. Now it does, so we
can remove this code.

Change-Id: I48604a2eb4ed854665c9c9a24ba7b03657fea116
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>