Remove Modin from Ray wheels. (#5647)

There are several reasons for this:

* We no longer support python2
* There should be only 1 way of installing Modin
  * Issue management on these wheels
* I have never heard of anyone using this feature
* It is rarely kept up to date
* Modin depends on specific versions of Ray because of past API changes

python/ray/__init__.py

@@ -53,9 +53,6 @@ except ImportError as e:
             e.args += (helpful_message, )
     raise
 
-modin_path = os.path.join(os.path.abspath(os.path.dirname(__file__)), "modin")
-sys.path.append(modin_path)
-
 from ray._raylet import (
     ActorCheckpointID,
     ActorClassID,

python/ray/tests/test_modin.py

@@ -1,25 +0,0 @@
-from __future__ import absolute_import
-from __future__ import division
-from __future__ import print_function
-
-import pytest
-
-import ray
-
-
-def test_modin_import_with_ray_init(shutdown_only):
-    ray.init(num_cpus=1)
-    import modin.pandas as pd
-    frame_data = [1, 2, 3, 4, 5, 6, 7, 8]
-    frame = pd.DataFrame(frame_data)
-    assert frame.sum().squeeze() == sum(frame_data)
-
-
-# The following can be activated once we have a modin release that
-# includes https://github.com/modin-project/modin/pull/472.
-@pytest.mark.skip(reason="needs #472 in modin")
-def test_modin_import(shutdown_only):
-    import modin.pandas as pd
-    frame_data = [1, 2, 3, 4, 5, 6, 7, 8]
-    frame = pd.DataFrame(frame_data)
-    assert frame.sum().squeeze() == sum(frame_data)