Improve deactivation modal styling

[gabrielcld2]

Some slight improvements to the deactivation modal. We want to make sure people are aware they don't have to submit a reason (we receive way too many "other reason" with no additional info).

Approach

• Make the "Skip and deactivate" link more visible by using a standard button styling. This means people are more aware of it and can lower the amount of empty "other reason" submissions
• Make the deactivation text as a proper heading with more visibility. This makes it clearer what the purpose of the modal is.

QA notes

• Go to the list of plugins
• Click on deactivate for the Cloudinary plugin
• Confirm the modal is shown as expected