Deprecate allow_nulls and forbid_nulls since they were duplicated met… #1142

Job	Run time
check_format	1m 22s
specs (shard.yml, 14, 1.10.0, false)	3m 46s
specs (shard.yml, 14, latest, false)	3m 26s
specs (shard.yml, 15, 1.10.0, false)	3m 56s
specs (shard.yml, 15, latest, false)	3m 19s
specs (shard.yml, 16, 1.10.0, false)	3m 56s
specs (shard.yml, 16, latest, false)	3m 26s
specs (shard.edge.yml, latest, 14, true)	3m 22s
specs (shard.override.yml, nightly, 14, true)	3m 50s
	30m 23s

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