py36+: remove TYPE_CHECKING from _pytest.compat

automated with:

```bash
git grep -l 'from .* import TYPE_CHECKING' |
    xargs reorder-python-imports \
        --application-directories .:src \
        --remove-import 'from _pytest.compat import TYPE_CHECKING' \
        --add-import 'from typing import TYPE_CHECKING'
```

testing/test_runner.py

@@ -5,6 +5,7 @@ import types
 from typing import Dict
 from typing import List
 from typing import Tuple
+from typing import TYPE_CHECKING
 
 import py
 
@@ -13,7 +14,6 @@ import pytest
 from _pytest import outcomes
 from _pytest import reports
 from _pytest import runner
-from _pytest.compat import TYPE_CHECKING
 from _pytest.config import ExitCode
 from _pytest.outcomes import OutcomeException