fix(test-schemathesis): disable rate limiter in fuzz subprocess

Schemathesis fires up to 3000 examples per endpoint. POST /auth/login
caps at 10/5min per IP, so the second example onward returns 429 and
the positive_data_acceptance check flags it as RejectedPositiveData
(its allowed-status list is hardcoded in schemathesis to
2xx/401/403/404/409/5xx, so OpenAPI tweaks can't fix it).

DECNET_LIMITER_ENABLED=false exists for exactly this case (see
limiter.py docstring on stress/load testing).

Reverts the custom_openapi shim from 5d88346 / 9b1168c — the endpoint
already declares 429 in its responses= map (api_login.py:38), and the
shim turned out to address a problem that wasn't there. Drop the
companion test along with it.

tests/api/test_schemathesis.py

@@ -94,6 +94,12 @@ def start_automated_server() -> subprocess.Popen:
     env["DECNET_DEVELOPER"] = "true"
     env["DECNET_CONTRACT_TEST"] = "true"
     env["DECNET_JWT_SECRET"] = TEST_SECRET
+    # Schemathesis fires thousands of examples per endpoint; the login
+    # bucket (10/5min per IP) trips on the second example and turns
+    # every subsequent valid request into a RejectedPositiveData
+    # failure. Disable the limiter for the fuzz subprocess — same
+    # rationale as the load-testing knob in decnet/web/limiter.py.
+    env["DECNET_LIMITER_ENABLED"] = "false"
 
     log_dir = Path(__file__).parent.parent.parent / "logs"
     log_dir.mkdir(exist_ok=True)