Do not mark test strings for translation

[David Planella]

While translating the app, I noticed some strings have got a path similar to this:

../library/uitest/ui/SignInPageDesign.qml:66

This leads me to believe that these strings are only used for testing purposes during development and are otherwise not shown to the user. If this is the case, I'd suggest to not put them in the final .pot file to save translator effort, as effectively their translations will not be used.

I can see two ways of doing this:

- Removing the i18n.tr() marker from the test files
- Alternatively, not include the test files to the list of files passed to xgettext in the CMakeLists.txt file

Probably the second is the least intrusive in terms of changes.