Remove trio.tests import causing warnings

It is deprecated and the replacement is made private as trio._tests.
While we could be using that, this commit copies over the one relevant
function that is actually necessary. The other two imports just repeat
tests that are already in trio and do not need repeating here.

pytest_trio/_tests/test_hypothesis_interaction.py

@@ -1,10 +1,5 @@
 import pytest
 import trio
-from trio.tests.test_scheduler_determinism import (
-    scheduler_trace,
-    test_the_trio_scheduler_is_not_deterministic,
-    test_the_trio_scheduler_is_deterministic_if_seeded,
-)
 from hypothesis import given, settings, strategies as st
 
 from pytest_trio.plugin import _trio_test_runner_factory
@@ -38,6 +33,22 @@ async def test_mark_and_parametrize(x, y):
     assert y in (1, 2)
 
 
+async def scheduler_trace():
+    """Returns a scheduler-dependent value we can use to check determinism."""
+    trace = []
+
+    async def tracer(name):
+        for i in range(10):
+            trace.append((name, i))
+            await trio.sleep(0)
+
+    async with trio.open_nursery() as nursery:
+        for i in range(5):
+            nursery.start_soon(tracer, i)
+
+    return tuple(trace)
+
+
 def test_the_trio_scheduler_is_deterministic_under_hypothesis():
     traces = []