OCSADV-154 Remove JNNNN, BNNNN, and Apparent "systems"

The whole notion of "systems" in the old target model is really very wrong, but at least we can simplify the problem by removing cases that are unused. This PR removes the `JNNNN`, `BNNNN`, and `Apparent` system types, leaving only J2000 and B1950. The B1950 targets be precessed to J2000 in another PR, leaving us with a single holy and true coordinate system.

Targets arriving via catalog that would be assigned `JNNNN` or `BNNNN` in the past now get `J2000` and `B1950` ... I am fairly sure this never happens as there are no such targets in either database.