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/python.py

@@ -23,6 +23,7 @@ from typing import Mapping
 from typing import Optional
 from typing import Set
 from typing import Tuple
+from typing import TYPE_CHECKING
 from typing import Union
 
 import py
@@ -49,7 +50,6 @@ from _pytest.compat import REGEX_TYPE
 from _pytest.compat import safe_getattr
 from _pytest.compat import safe_isclass
 from _pytest.compat import STRING_TYPES
-from _pytest.compat import TYPE_CHECKING
 from _pytest.config import Config
 from _pytest.config import ExitCode
 from _pytest.config import hookimpl