Improve Delay JavaScript Execution UI when no plugin / theme are detected

[WordPresseur]

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Describe the bug When there's no plugin or theme detected by the Delay JavaScript Execution, the related One-Click exclusion section won't be displayed:

To Reproduce Steps to reproduce the behavior:

1. Go to Theme & Plugins and deactivate all the know themes & plugins
2. Go to Delay JavaScript Execution One-Click exclusion sections
3. See UI issue

Expected behavior It could show that No known plugin/theme were found:

Additional context HS ticket: https://secure.helpscout.net/conversation/2210737089/413692?folderId=1213662

Backlog Grooming (for WP Media dev team use only)

• [ ] Reproduce the problem
• [ ] Identify the root cause
• [ ] Scope a solution
• [ ] Estimate the effort

[camilamadronero]

Or, we could dynamically change the text:

• If we detect everything: If you are using any of the following plugins/themes/services you can prevent that, by selecting them below.
• If we detect plugins only: If you are using any of the following plugins you can prevent that, by selecting them below.
• If we detect services only: If you are using any of the following services you can prevent that, by selecting them below.

And so on.