Remove limit from fetching data for data export

[merkushin]

Resolves #7629

When we export student progress by a course, when the course has many lessons (more than 10), we miss part of the progress in exported data.
That happens because of the default limit (normally, 10) for the query that fetches data.

Proposed Changes

• Remove the limit from fetching data for data export.

Testing Instructions

1. Create a course with at least 10 lessons. (Simplest thing would be to import and publish the demo course.)
2. As a student, start taking the course.
3. Browse to wp-admin/admin.php?page=sensei_reports&user_id=<user_id>&course_id=<course_id> for the given user and course ID.
4. Export all rows.
5. Make sure CSV contains data for all lessons you took as the student.

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Acceptance criteria is met
• Decisions are publicly documented
• 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
• New UIs match the designs
• Different user privileges (admin, teacher, subscriber) are tested as appropriate
• Legacy courses (course without blocks) are tested
• Code is tested on the minimum supported PHP and WordPress versions
• User interface changes have been tested on the latest versions of Chrome, Firefox and Safari
• "Needs Documentation" label is added if this change requires updates to documentation
• Known issues are created as new GitHub issues

[merkushin]

@donnapep
Here, I removed the limit completely to allow export all existing data (even if there are 100000 rows). This is how I get “Export all rows”.
On the other hand, we can read “Export all rows” as “Export all visible rows”. In this case, we need to apply the same limit we use on the page.

[merkushin]

I noticed that in another place we already removed the limit: https://github.com/Automattic/sensei/blob/trunk/includes/reports/overview/list-table/class-sensei-reports-overview-list-table-abstract.php#L179

[github-actions]

Test the previous changes of this PR with WordPress Playground.

[github-actions]

Test the previous changes of this PR with WordPress Playground.

[m1r0]

LGTM!

I'm not concerned that the server will be running out of memory because of too many lessons. It seems unlikely and should be considered as an edge case.