cleanup legacy Querier iterators code (take 1) #8539

Job	Run time
CodeQL	10m 15s
test	19m 32s
lint	2m 15s
build	4m 30s
integration-configs-db	2m 2s
integration (requires_docker)	5m 36s
integration (integration_alertmanager)	3m 58s
integration (integration_backward_compatibility)	7m 51s
integration (integration_memberlist)	7m 39s
integration (integration_querier)	12m 35s
integration (integration_ruler)	3m 48s
integration (integration_query_fuzz)	2m 0s
deploy_website	0s
deploy	0s
	1h 22m 1s

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