Revert: use the new form of QTranslator::load() for more flexibility

This reverts commit 427646b8d7c52e5b84240e07ffd391217ce3bfa8.
It seems that it should have been more correct, but we are still not
shipping English translations, and static QString find_translation()
in qtranslator.cpp will return any language which is in
QLocale::uiLanguages() for which the translation file is found.
That is a long list on OSX.

Reverting the patch means find_translation() is not called in
such cases.  This change can be re-done whenever we are more sure
that the attempt to find a translation will succeed in finding a
sensible one, or fall back to not translating, rather than choosing
a language that the user didn't intend.

Task-number: QTBUG-41977
Change-Id: I425946cc71cec96b4f38629eb2b7e80220c5236d
Reviewed-by: Jan Arve Sæther <jan-arve.saether@theqtcompany.com>