Drop ipywidgets and ocs_widgets

[BrianJKoopman]

Description

Drop the old ipywidgets based ocs_widgets.

Motivation and Context

Since @jlashner said these should be forgotten.

How Has This Been Tested?

Only removals. Tests still pass.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• Unless I am preparing a release, I have opened this PR onto the develop branch.