fix: delete dead PYAUTOFIT_TEST_MODE fixture in aggregator conftest (#95)

The autouse `set_test_mode` fixture set `PYAUTOFIT_TEST_MODE`, which nothing
reads — the canonical knob is `PYAUTO_TEST_MODE` (autonerves/test_mode.py).
The fixture has therefore always been a silent no-op.

Renaming it to the live variable is NOT the right fix: it makes test mode
actually take effect, which bypasses sampling so the aggregator has no samples
to iterate, and 6 of the 13 aggregator tests fail. These tests were written
against — and only pass under — normal sampling.

Verified three ways:
  dead var present (baseline) -> 13 passed
  renamed to PYAUTO_TEST_MODE -> 6 failed, 7 passed
  fixture deleted (this fix)  -> 13 passed

So the fixture is deleted rather than renamed: behaviour-preserving, and it
removes a trap that autocti_workspace_test/AGENTS.md and autocti_assistant
had resorted to documenting instead of deleting.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JiU4VbBD9X6jPYJMCx3boh

Author: 2 people

test_autocti/aggregator/conftest.py

@@ -10,13 +10,6 @@
 from autofit.non_linear.samples import Sample
 
 
-@pytest.fixture(autouse=True)
-def set_test_mode():
-    os.environ["PYAUTOFIT_TEST_MODE"] = "1"
-    yield
-    del os.environ["PYAUTOFIT_TEST_MODE"]
-
-
 def clean(database_file):
     database_sqlite = path.join(conf.instance.output_path, f"{database_file}.sqlite")