Drop private imports from test_exported_members.py (#2573)

Co-authored-by: Tom Christie <tom@tomchristie.com>

tests/test_exported_members.py

@@ -1,10 +1,9 @@
 import httpx
-from httpx import __all__ as exported_members
 
 
 def test_all_imports_are_exported() -> None:
     included_private_members = ["__description__", "__title__", "__version__"]
-    assert exported_members == sorted(
+    assert httpx.__all__ == sorted(
         (
             member
             for member in vars(httpx).keys()