Deprecated properties no longer cause errors when validating.

Checklist

[x] This PR adds an entry to the CHANGELOG. _See https://keepachangelog.com/en/1.0.0/ for instructions. Minor edits are exempt.
[ ] This PR expects some manual changes to the generated code. The needed changes are detailed in the CHANGELOG entry.
[X] This PR was tested with at least one code generation, resulting in a working OSLC server.
[x] This PR does NOT break the user block code

Closes #223