net-mgmt/netbox: Fix build after a06fe6e3

* Remove the py-jsonschema dependency with its fixed version range that
  was required as a temporary workaround by upstream because releases
  of devel/py-swagger-spec-validator before 2.7.4, which are required by
  www/py-dj32-drf-yasg, were not compatible with jsonschema 4.x.

* Bump PORTREVISION due changed dependencies.