Remove Drupal 8

[rosiel]

GitHub Issue: (link)

Discussed at June 29 Tech Call

What does this Pull Request do?

Removes Drupal 8 from the module's info.yml file (and description in the composer file)

What's new?

• Removed D8
• Does this change require documentation to be updated? - no, this includes some
• Does this change add any new dependencies? - no
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)? no
• Could this change impact execution of existing code? no

How should this be tested?

A description of what steps someone could take to:

• Reproduce the problem you are fixing (if applicable)
• Test that the Pull Request does what is intended.
• Please be as detailed as possible.
• Good testing instructions help get your PR completed faster.

Additional Notes:

Any additional information that you think would be helpful when reviewing this
PR.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora/8-x-committers