windeployqt: Make --no-translations work for QtWebEngine

The --no-translations option was deliberately ignored for QtWebEngine,
because of crashes when translations were missing. The crashes have been
fixed, but QtWebEngine still expects at least one translation file.
Otherwise it will warn in the debug log.

Now, when passing --no-translations only the en-US.pak translation file
will be deployed.

Task-number: QTBUG-51658
Change-Id: I767cf74c728e51bed30a94c47948f27f9b801999
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>