Remove obsolete code from Students area

[donnapep]

Resolves https://github.com/Automattic/sensei-security/issues/19.

Proposed Changes

While working on #7724, I noticed that code that used to run in the Students area when the URL had the view=courses query parameter, or when the URL had no view parameter, appears to be obsolete. I clicked through all of the Students screens and was unable to find an instance where there was no view parameter or where view was set to courses.

I then reverted Sensei to version 4.3, which is the release prior to the one in which we overhauled Learner Management. In that version, the default screen that displayed when clicking Student Management did indeed set the view property to courses and execute this code. So I think we just missed removing this obsolete code back then, and I'm going ahead and ripping the bandaid off now. 😬

Testing Instructions

1. Try to click through all of the Students area to see if anything breaks, including Bulk Actions.
2. Click through other areas of Sensei just in case.

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• Code is tested on the minimum supported PHP and WordPress versions

[github-actions]

Test the previous changes of this PR with WordPress Playground.

[github-actions]

Test the previous changes of this PR with WordPress Playground.