[CLEANUP] Remove old code that supported old ember-test-helpers #9932

Job	Run time
Basic Test	1m 26s
Type Checking (current version)	1m 1s
Linting	1m 13s
Type Checking (other supported versions) (4.9)	1m 10s
Type Checking (other supported versions) (5.0)	1m 3s
Type Checking (other supported versions) (5.1)	1m 6s
Type Checking (other supported versions) (5.2)	1m 15s
Type Checking (other supported versions) (5.3)	1m 7s
Blueprint Tests	9m 35s
Node.js Tests	1m 4s
Browser Tests (Firefox)	1m 55s
Browserstack Tests (Safari, Edge)	5m 9s
All deprecations enabled	1m 33s
Smoke tests (Full Ember Apps) (classic-basics)	1m 22s
All deprecations enabled, with optional features	1m 29s
Smoke tests (Full Ember Apps) (embroider-basics)	1m 24s
Deprecations as errors	1m 50s
Deprecations as errors, with optional features	1m 30s
Production build	1m 42s
Production build, with optional features	1m 32s
Deploy tags to npm	0s
Publish channel to s3	0s
Notify Discord	0s
Publish alpha from default branch	0s
	39m 26s

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