Remove checks for /$reference?level=...

[mjacoby]

Currently there are checks testing with content modifier reference in combination with level, e.g.

/shells/d3d3LmV4YW1wbGUuY29tL2lkcy9hYXMvODEzMl80MTAyXzgwNDJfNzU2MQ==/submodels/d3d3LmV4YW1wbGUuY29tL2lkcy9zbS84MTMyXzQxMDJfODA0Ml8xODYx/submodel-elements/$reference?level=core

Although this is allowed according to the specification it does not make any sense as the level modifier cannot influence the result.
According to the TF API this is a copy & paste error and the argument should have never been there.
This has been reflected by setting the level parameter as deprecated for calls to /$reference (as it could not be safely deleted without causing a breaking chance).

Therefore, I think these tests should be excluded in the future.

[otto-ifak]

Thank you, we will change this accordingly.