Remove legacy case study code [WHIT-3250] #18750

Job	Run time
CodeQL SAST scan / Analyze	2m 13s
Lint SCSS / Run Stylelint	19s
Prettier / Run Prettier	24s
Lint JavaScript / Run Standardx	20s
Test Ruby / assets-required-1	3m 6s
Security Analysis / Run Brakeman	28s
Dependency Review scan / dependency-review-pr	6s
Test Ruby / assets-required-0	2m 16s
Test JavaScript / Run Jasmine	39s
Test Ruby / ruby-only-0	2m 42s
Lint ERB / Run ERB lint	38s
Test Ruby / ruby-only-1	3m 10s
Test features / Test features / non-javascript-1	2m 4s
Test features / Test features / non-javascript-0	2m 16s
Lint Ruby / Run RuboCop	34s
Test features / Test features / javascript-0	2m 40s
Test features / Test features / non-javascript-2	2m 11s
Dependency Review scan / dependency-review-push	0s
Test features / Run Cucumber	0s
Test Ruby / Run Minitest	3s
notify-slack-if-failure-on-main	0s
	26m 9s

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