Remove "Customize your lesson template" task

[donnapep]

Resolves #7508.

Proposed Changes

Removes the "Customize your lesson template" task from the task list.

Testing Instructions

1. Enable the Course theme.
2. Execute the following SQL - delete from wp_options where option_name like '%sensei_home_task_%.
3. Go to Sensei LMS > Home.
4. Check that there is no "Customize your lesson template" in the task list.
5. Ensure the progress is calculated correctly.

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

[github-actions]

Test the previous changes of this PR with WordPress Playground.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.92%. Comparing base (83e8eda) to head (8450ab6).
Report is 1 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk    #7539      +/-   ##
============================================
- Coverage     51.93%   51.92%   -0.02%     
+ Complexity    11277    11265      -12     
============================================
  Files           631      630       -1     
  Lines         47710    47683      -27     
  Branches        421      421              
============================================
- Hits          24779    24759      -20     
+ Misses        22594    22587       -7     
  Partials        337      337              

Files	Coverage Δ
...in/home/tasks/class-sensei-home-tasks-provider.php	83.14% <ø> (-0.38%)	⬇️
includes/class-sensei-admin.php	12.11% <ø> (+0.06%)	⬆️

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