Clean up `EMBER_TYPESCRIPT_BLUEPRINTS` feature flag #9994

Job	Run time
Linting	8s
Basic Test	8s
Type Checking (current version)	9s
Type Checking (other supported versions)	0s
${{ matrix.name }}	0s
Blueprint Tests	0s
Node.js Tests	0s
Browserstack Tests (Safari, Edge)	0s
Smoke tests (Full Ember Apps)	0s
Browser Tests (Firefox)	0s
Deploy tags to npm	0s
Publish channel to s3	0s
Notify Discord	0s
Publish alpha from default branch	0s
	25s

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