Remove dj.kill and dj.kill_quick #1347

Summary

Propose removing dj.kill() and dj.kill_quick() from DataJoint. These functions are database administration utilities that don't belong in a data pipeline library.

Reasoning

1. Outside DataJoint's scope

DataJoint's purpose is defining schemas and managing scientific data pipelines — not database administration. Connection management is a DBA task with dedicated tools.

2. Better alternatives exist

Users sophisticated enough to need connection killing can use these purpose-built tools.

3. Current implementation has issues

• Interactive prompts — input() makes it unusable in scripts/automation
• SQL injection risk — string interpolation into queries
• MySQL-only — won't work with PostgreSQL backend
• Maintenance burden — supporting across backends adds complexity for marginal value

4. Security consideration

Killing database connections is a privileged operation. Exposing it as a casual dj.kill() call may encourage inappropriate use.

5. The real problem is job management

The main use case is killing stuck populate() jobs. This is better addressed by:

• Job timeouts
• Graceful cancellation mechanisms
• Better job monitoring

...rather than raw connection termination.

Proposal

1. Deprecate dj.kill() and dj.kill_quick() with warning in next minor release
2. Remove in next major version
3. Document alternatives in migration guide

Alternatives for users

-- MySQL: List and kill connections
SHOW PROCESSLIST;
KILL 1234;

-- PostgreSQL: List and kill connections
SELECT pid, usename, state, query FROM pg_stat_activity WHERE pid <> pg_backend_pid();
SELECT pg_terminate_backend(1234);