Imagify transients shall be removed after deleting imagify

[Mai-Saad]

Before submitting an issue please check that you’ve completed the following steps:

• Made sure you’re on the latest version => 2.2.3.2
• Used the search feature to ensure that the bug hasn’t been reported before

Describe the bug
After deleting the plugins these transients still not removed

To Reproduce
Steps to reproduce the behavior:

1. Fresh install and activation
2. access settings page
3. deactivate/ delete imagify

Expected behavior
A clear and concise description of what you expected to happen.
All imagify transients are removed

Screenshots
If applicable, add screenshots to help explain your problem.

Acceptance Criteria (for WP Media team use only)
Clear instructions for developers, to be added before the grooming