Remove deprecated drupal-project docs.

[rosiel]

Purpose / why

This page made reference to a drupal-project architecture that we deprecated a while ago. This page was needed because we maintained our own fork with some Islandora customizations.

We now use drupal/core-recommended as we are supposed to, so this page can be removed. https://github.com/drupal/core-recommended#drupalcore-recommended

What changes were made?

Removed the page on updating drupal-project

Verification

Is the page out of date and now irrelevant?

Interested Parties

• @jordandukart
• @Islandora/documentation

Checklist

Pull-request Reviewer

Pull-request reviewer should ensure the following:

• Does this PR link to related issues?
• Does the proposed documentation align with the Islandora Documentation Style Guide?
• Are the changes accurate, useful, free of typos, etc?

Person Merging

The person merging should ensure the following:

• Does mkdocs still build successfully? (This is indicated by TravisCI passing. To test locally, and see warnings, see How To Build Documentation.)
• If pages are renamed or removed, have all internal links to those pages been fixed?
• If pages are added, have they been linked to or placed in the menu?
• Did the PR receive at least one approval from a committer, and all issues raised have been addressed?