Rebased #1950 on current master: Cleanup all the plugins

[seefood]

code by @gaelicWizard , manually rebased on latest master by @seefood

Description

This is my work-in-progress branch with all the plugins cleanup.

Motivation and Context

This branch is based on my shellcheck (#1917) and command_duration (#1906) branches, so the changes here are entirely within the plugins section.

How Has This Been Tested?

My main branch is based on this branch.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the code style of this project.
• [ ] If my change requires a change to the documentation, I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
• [ ] I have added tests to cover my changes, and all the new and existing tests pass.