Remove opinionated CSS class from login form

[donnapep]

Resolves https://wordpress.org/support/topic/class-alignwide-is-hardcoded-in-output-of-my-courses-content/.

Proposed Changes

We shouldn't be using the alignwide class on the login form. Ideally, the login form should be the same width as the rest of the site's content.

Testing Instructions

1. Navigate to the My Courses page as a logged out user.
2. Check that the login form is the same width as page / post content.
3. Test on different themes.

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 51.82%. Comparing base (46c9479) to head (3be3259).
Report is 38 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk    #7542      +/-   ##
============================================
- Coverage     51.92%   51.82%   -0.10%     
- Complexity    11265    11307      +42     
============================================
  Files           630      640      +10     
  Lines         47683    47979     +296     
  Branches        421      446      +25     
============================================
+ Hits          24759    24865     +106     
- Misses        22587    22755     +168     
- Partials        337      359      +22     

Files	Coverage Δ
includes/class-sensei-frontend.php	17.76% <100.00%> (ø)

... and 1 file with indirect coverage changes

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