Issue 698 no drops

[mariacha]

For the PR creator:

Check off the following boxes before asking someone to review this PR.

• [x] If this PR changes the composer.json file, is there accompanying text in the README.md file explaining that change?
• [x] Update the "How to test this branch" instructions below by replacing [the-branch] with the name of this branch, and [the-new-project] with an example project name.

What this PR does:

• A few composer changes to make new site spinups work without requiring the example drops repo. Also updates to php 7.4. Related PR: https://github.com/United-Philanthropy-Forum/km-collaborative/pull/713
• I'm also giving up on keeping track of the changes to the composer.json file, because they're extensive and largely unhelpful at this point. There's always git blame/history to find out what's happened to the file.

How to test this branch:

• [x] If you haven't already, run the One time setup steps
• [x] Run this:

COMPOSER_MEMORY_LIMIT=-1 terminus build:project:create --team='United Philanthropy Forum' --org='United-Philanthropy-Forum' --visibility='private' --stability=dev "united-philanthropy-forum/km-starter-kit:dev-issue-698-no-drops" drops-out3

• [x] Validate that a new site exists at https://dev-drops-out3.pantheonsite.io -- and that it's running php 7.4
• [x] Validate the repo exists at https://github.com/United-Philanthropy-Forum/drops-out3
• [x] Delete the test environment when you're done, by running terminus build:env:obliterate drops-out3
• [x] Merge the km-collaborative pr: https://github.com/United-Philanthropy-Forum/km-collaborative/pull/713
• [x] Wait for the release containing ^ to be merged.
• [x] Cut a new tag on this project so the create-project commands will get the latest and greatest.
• [ ] In KM-collab, make sure there are no lingering references to this branch in the .circleci/config.yml file, like in this PR: https://github.com/United-Philanthropy-Forum/km-collaborative/pull/728

[unclegcb]

https://github.com/United-Philanthropy-Forum/km-starter-kit/releases/tag/v1.0.0