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'
```

src/_pytest/mark/expression.py

@@ -23,11 +23,10 @@ from typing import Iterator
 from typing import Mapping
 from typing import Optional
 from typing import Sequence
+from typing import TYPE_CHECKING
 
 import attr
 
-from _pytest.compat import TYPE_CHECKING
-
 if TYPE_CHECKING:
     from typing import NoReturn