chore: remove export_count legacy alias from export state API #129

Job	Run time
mypy	15s
Verify prod requirements.txt is sufficient	6s
pytest (ubuntu-latest)	15s
pytest (windows-latest)	1m 3s
API integration tests + coverage (ubuntu-latest)	16s
API integration tests + coverage (windows-latest)	38s
Frontend unit tests (vitest) (ubuntu-latest)	17s
Frontend unit tests (vitest) (windows-latest)	43s
	3m 33s

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