Removes unused field #3511

Job	Run time
Setup Build Matrix (true, ion-rust, windows, macos, ubuntu, al2-x86, al2-arm, windows, macos, ubu...	1s
Build and Test (windows, default)	4m 36s
Build and Test (windows, all)	6m 21s
Build and Test (windows, experimental-ion-hash)	5m 52s
Build and Test (windows, experimental)	6m 43s
Build and Test (macos, default)	1m 38s
Build and Test (macos, all)	3m 10s
Build and Test (macos, experimental-ion-hash)	2m 40s
Build and Test (macos, experimental)	2m 18s
Build and Test (ubuntu, default)	1m 50s
Build and Test (ubuntu, all)	3m 41s
Build and Test (ubuntu, experimental-ion-hash)	1m 55s
Build and Test (ubuntu, experimental)	2m 58s
Build and Test (al2-x86, default)	1m 23s
Build and Test (al2-x86, all)	13m 30s
Build and Test (al2-x86, experimental-ion-hash)	1m 27s
Build and Test (al2-x86, experimental)	13m 10s
Build and Test (al2-arm, default)	1m 36s
Build and Test (al2-arm, all)	2m 6s
Build and Test (al2-arm, experimental-ion-hash)	1m 26s
Build and Test (al2-arm, experimental)	13m 28s
Build and Test Confirmation	1s
	1h 31m 50s

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