feat: remove dj.kill and dj.kill_quick

Remove database connection management functions that don't belong in a
data pipeline library.

Closes #1347

Reasoning:
- Outside DataJoint's scope (data pipelines, not DB administration)
- Better tools exist (native SQL, CLI tools, GUIs, cloud consoles)
- Implementation had issues (interactive prompts, SQL injection risk)
- MySQL-only, wouldn't work with PostgreSQL backend

Users can use native database tools instead:
- MySQL: SHOW PROCESSLIST; KILL <pid>;
- PostgreSQL: SELECT * FROM pg_stat_activity; SELECT pg_terminate_backend(pid);

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/__init__.py

@@ -39,7 +39,6 @@
     "Top",
     "U",
     "Diagram",
-    "kill",
     "MatCell",
     "MatStruct",
     # Codec API
@@ -94,8 +93,6 @@
     # Diagram imports networkx and matplotlib
     "Diagram": (".diagram", "Diagram"),
     "diagram": (".diagram", None),  # Return the module itself
-    # kill imports pymysql via connection
-    "kill": (".admin", "kill"),
     # cli imports click
     "cli": (".cli", "cli"),
 }

src/datajoint/admin.py

@@ -27,25 +27,6 @@ def test_lazy_diagram_import():
     assert Diagram.__name__ == "Diagram"
 
 
-def test_lazy_admin_import():
-    """Admin module should not be loaded until dj.kill is accessed."""
-    # Remove datajoint from sys.modules to get fresh import
-    modules_to_remove = [key for key in sys.modules if key.startswith("datajoint")]
-    for mod in modules_to_remove:
-        del sys.modules[mod]
-
-    # Import datajoint
-    import datajoint as dj
-
-    # Admin module should not be loaded yet
-    assert "datajoint.admin" not in sys.modules, "admin module loaded eagerly"
-
-    # Access kill - should trigger lazy load
-    kill = dj.kill
-    assert "datajoint.admin" in sys.modules, "admin module not loaded after access"
-    assert callable(kill)
-
-
 def test_lazy_cli_import():
     """CLI module should not be loaded until dj.cli is accessed."""
     # Remove datajoint from sys.modules to get fresh import
@@ -103,5 +84,4 @@ def test_core_imports_available():
 
     # Heavy modules should still not be loaded
     assert "datajoint.diagram" not in sys.modules
-    assert "datajoint.admin" not in sys.modules
     assert "datajoint.cli" not in sys.modules