Don't upsert work item types if not found on the DB

In [Discussion] How to handle required work item t... (#423483) we discussed being able to rely on DB seeds and migrations for data that we expect to exist on the BD prior to application's first run. The conclusion was that we should be able to do so as some parts of the application already rely on this. For issue creation/update we have a mechanism that will create missing work item types and widget definitions if the specified type is not found. We should remove this part of the code and simply expect that the application has been seeded correctly for new installs.