Remove unnecessary checkCast calls #9237

Job	Run time
Build Ballerina Lang	8m 8s
Build Ballerina Distribution	52m 2s
Build Stdlib Level (1)	5m 14s
Build Stdlib Level (10)	5m 8s
Build Stdlib Level (2)	14m 12s
Build Stdlib Level (3)	9m 45s
Build Stdlib Level (4)	17m 4s
Build Stdlib Level (5)	6m 51s
Build Stdlib Level (7)	21m 17s
Build Stdlib Level (6)	35m 18s
Build Stdlib Level (8)	29m 14s
Build Stdlib Level (9)	1h 14m 39s
	4h 38m 52s

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