Remove `string_to_utc_time` conversion function #531

Job	Run time
Ruby specs (3.0, rails_7.0, stable)	1m 32s
Ruby specs (3.0, rails_7.0, stable)	1m 32s
Ruby specs (3.0, rails_7.1, stable)	1m 41s
Ruby specs (3.0, rails_7.1, stable)	1m 41s
Ruby specs (3.1, rails_7.0, stable)	1m 31s
Ruby specs (3.1, rails_7.0, stable)	1m 31s
Ruby specs (3.1, rails_7.1, stable)	1m 36s
Ruby specs (3.1, rails_7.1, stable)	1m 36s
Ruby specs (3.2, rails_7.0, stable)	1m 48s
Ruby specs (3.2, rails_7.0, stable)	1m 48s
Ruby specs (3.2, rails_7.1, stable)	1m 36s
Ruby specs (3.2, rails_7.1, stable)	1m 36s
Ruby specs (3.3, rails_7.0, stable)	2m 2s
Ruby specs (3.3, rails_7.0, stable)	2m 2s
Ruby specs (3.3, rails_7.1, stable)	2m 3s
Ruby specs (3.3, rails_7.1, stable)	2m 3s
Ruby specs (3.1, rails_edge, experimental)	2m 8s
Ruby specs (3.1, rails_edge, experimental)	2m 8s
Ruby specs (3.2, rails_edge, experimental)	1m 34s
Ruby specs (3.2, rails_edge, experimental)	1m 34s
Ruby specs (head, rails_7.0, experimental)	42s
Ruby specs (head, rails_7.0, experimental)	42s
Ruby specs (head, rails_7.1, experimental)	2m 14s
Ruby specs (head, rails_7.1, experimental)	2m 14s
Ruby specs (head, rails_edge, experimental)	2m 30s
Ruby specs (head, rails_edge, experimental)	2m 17s
	45m 41s

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