improvement: remove unused data in subscription batcher (#227) #1204

Job	Run time
ash-ci / mix deps.get	15s
ash-ci / MIX_ENV=test mix.compile	48s
ash-ci / audit	37s
ash-ci / MIX_ENV=dev mix.compile	37s
ash-ci / mix docs	31s
ash-ci / mix spark.formatter --check	44s
ash-ci / mix dialyzer	3m 41s
ash-ci / mix credo --strict	50s
ash-ci / mix ash.codegen --check	0s
ash-ci / mix format --check-formatted	45s
ash-ci / mix sobelow	39s
ash-ci / mix spark.cheat_sheets --check	40s
ash-ci / mix test	1m 22s
ash-ci / mix deps.unlock --check-unused	42s
ash-ci / Deploy docs to GitHub pages.	9s
ash-ci / Release	0s
	12m 20s

Provide feedback