Remove `Relation#build_preloader` #599

Job	Run time
Ruby specs (3.0, rails_7.0, 16, stable)	1m 28s
Ruby specs (3.0, rails_7.1, 16, stable)	1m 30s
Ruby specs (3.1, rails_7.0, 16, stable)	1m 21s
Ruby specs (3.1, rails_7.1, 16, stable)	1m 30s
Ruby specs (3.2, rails_7.0, 16, stable)	1m 29s
Ruby specs (3.2, rails_7.1, 16, stable)	1m 25s
Ruby specs (3.3, rails_7.0, 16, stable)	1m 52s
Ruby specs (3.3, rails_7.1, 16, stable)	1m 54s
Ruby specs (3.0, rails_7.0, 12, stable)	1m 18s
Ruby specs (3.1, rails_edge, 16, experimental)	1m 49s
Ruby specs (3.2, rails_edge, 16, experimental)	1m 36s
Ruby specs (3.3, rails_edge, 16, experimental)	2m 11s
Ruby specs (head, rails_7.0, 16, experimental)	35s
Ruby specs (head, rails_7.1, 16, experimental)	2m 11s
Ruby specs (head, rails_edge, 16, experimental)	2m 3s
	24m 12s

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