refactor: remove unused error variants #19572

Job	Run time
Check typos and docs	6s
Check (windows-2022)	9m 20s
Build GreptimeDB binary (profile-CI) (ubuntu-20.04)	2m 50s
Check (ubuntu-20.04)	2m 0s
Build GreptimeDB binaries (ubuntu-20.04)	3m 2s
Clippy	3m 30s
Rustfmt	48s
Check License Header	2m 10s
Toml Check	27s
coverage	14m 6s
Unstable Fuzz Test (unstable_fuzz_create_table_standalone)	6m 23s
Fuzz Test with Chaos (Distributed, Remote WAL, fuzz_migrate_mito_regions)	8m 12s
Fuzz Test (Distributed, Remote WAL, fuzz_create_table)	9m 39s
Fuzz Test with Chaos (Distributed, Remote WAL, fuzz_failover_mito_regions)	8m 16s
Fuzz Test (Distributed, Remote WAL, fuzz_alter_table)	8m 50s
Fuzz Test with Chaos (Distributed, Remote WAL, fuzz_failover_metric_regions)	8m 17s
Fuzz Test (Distributed, Remote WAL, fuzz_create_database)	9m 34s
Fuzz Test (Distributed, Remote WAL, fuzz_create_logical_table)	14m 51s
Fuzz Test (Distributed, Remote WAL, fuzz_alter_logical_table)	8m 56s
Fuzz Test (Distributed, Remote WAL, fuzz_insert)	9m 19s
Fuzz Test (Distributed, Remote WAL, fuzz_insert_logical_table)	8m 49s
Sqlness Test (Basic)	2m 32s
Sqlness Test (Remote WAL)	2m 47s
Fuzz Test (fuzz_create_table)	7m 4s
Fuzz Test (fuzz_alter_table)	7m 13s
Fuzz Test (fuzz_create_database)	6m 22s
Fuzz Test (fuzz_create_logical_table)	7m 4s
Fuzz Test (fuzz_alter_logical_table)	6m 21s
Fuzz Test (fuzz_insert)	7m 20s
Fuzz Test (fuzz_insert_logical_table)	7m 37s
	3h 13m 45s

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