Remove calls to no-op routines in ensemble manager

[ann-norcio]

Description:

Removed the following no-op routines form ensemble manager: prepare_to_write_to_vars, prepare_to_write_to_copies, &
prepare_to_read_from_vars, prepare_to_read_from_copies, prepare_to_update_vars, &
prepare_to_update_copies

Fixes issue

#620

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)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Ran build_everything for all compilers. Tests passed, excluding known failures when running all quickbuilds.

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

[hkershaw-brown]

HI Anne, I'm going to close this pull request since its failing the 3 GitHub action checks. Let's chat about how you're testing this at out meeting today.

Cheers,
Helen