Remove the 19 unreferenced PropertyNameConstants

### Task Summary

`PropertyNameConstants` declares 21 constants; only two are referenced anywhere outside its own spec.

`LogicalOp` uses `OPERATOR_ID` and `OPERATOR_VERSION` as `@JsonProperty` annotation arguments — those are live and stay. Each of the other 19 has exactly three references, all inside `PropertyNameConstantsSpec`, and none anywhere else in the repository.

**Provenance.** The object arrived with the original amber import (2020-08-20) as the single source of truth for operator-JSON key names. Operator descriptors never adopted it: they spell their JSON keys as raw string literals, and the wire format is anchored elsewhere — `@JsonTypeInfo(property = "operatorType")` in `LogicalOp`, and literals in `OperatorMetadataGenerator` and `WorkflowResource`. So these constants were never the source of truth they were meant to be, and deleting them cannot change the protocol.

`TABLE_NAME` is included: its only qualified references are in the spec. The bare `TABLE_NAME` hits elsewhere are an unrelated SQL placeholder in `sql/misc/tweets.sql`.

Pure deletion, no behaviour change: −95 lines.

### Task Type

- [x] Refactor / Cleanup