Add mod_quiz\tests\attempt_walkthrough_testcase to unittestclasses

[junpataleta]

Adding from MDL-81521.
Also removing the test cases that are now seemingly unused:

• mod_quiz_attempt_walkthrough_from_csv_testcase
• mod_quiz\attempt_walkthrough_from_csv_test

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.82%. Comparing base (87c1bf8) to head (12e4088).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #321      +/-   ##
==========================================
- Coverage   31.07%   29.82%   -1.25%     
==========================================
  Files          71       71              
  Lines        3215     3215              
==========================================
- Hits          999      959      -40     
- Misses       2216     2256      +40     

Flag	Coverage Δ
check_upgrade_savepoints	0.46% <ø> (ø)
checkstyle_manipulations	0.00% <ø> (ø)
compare_databases	2.39% <ø> (ø)
continuous_manage_queues_validation	0.71% <ø> (ø)
define_excluded	1.11% <ø> (ø)
detect_conflicts	1.49% <ø> (ø)
diff_extract_changes	0.00% <ø> (ø)
grunt_process	3.01% <ø> (ø)
illegal_whitespace	2.64% <ø> (ø)
list_valid_components	0.00% <ø> (ø)
mustache_lint	2.83% <ø> (ø)
mustache_lint_plugins	1.30% <ø> (ø)
php_lint	1.21% <ø> (ø)
prepare_npm_stuff	1.52% <ø> (ø)
remote_branch_checker	17.48% <ø> (ø)
remote_branch_reporter	0.00% <ø> (ø)
setup	0.00% <ø> (ø)
thirdparty_check	1.46% <ø> (ø)
travis-branch-checker	0.00% <ø> (ø)
upgrade_external_backup	1.61% <ø> (ø)
verifications	0.00% <ø> (ø)
verify_commit_messages	2.64% <ø> (ø)
verify_phpunit_xml	?
versions_check_set	5.03% <ø> (ø)

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[junpataleta]

Closing in lieu of #322 .