Remove the file existence check in TorchCheckpointIO #7790

Job	Run time
fabric-cpu (macOS-11, lightning, 3.9, 1.12)	5m 44s
fabric-cpu (macOS-11, lightning, 3.10, 1.13)	6m 7s
fabric-cpu (ubuntu-20.04, lightning, 3.9, 1.12)	5m 12s
fabric-cpu (ubuntu-20.04, lightning, 3.10, 1.13)	5m 24s
fabric-cpu (windows-2022, lightning, 3.9, 1.12)	5m 24s
fabric-cpu (windows-2022, lightning, 3.10, 1.13)	5m 58s
fabric-cpu (macOS-11, lightning, 3.10, 2.0)	7m 20s
fabric-cpu (ubuntu-20.04, lightning, 3.10, 2.0)	6m 8s
fabric-cpu (windows-2022, lightning, 3.10, 2.0)	5m 48s
fabric-cpu (macOS-11, lightning, 3.11, 2.1)	6m 43s
fabric-cpu (ubuntu-20.04, lightning, 3.11, 2.1)	6m 31s
fabric-cpu (windows-2022, lightning, 3.11, 2.1)	6m 16s
fabric-cpu (macOS-12, fabric, 3.11, 2.0)	7m 26s
fabric-cpu (ubuntu-22.04, fabric, 3.11, 2.0)	7m 2s
fabric-cpu (windows-2022, fabric, 3.11, 2.0)	6m 16s
fabric-cpu (macOS-12, fabric, 3.11, 2.1)	7m 15s
fabric-cpu (ubuntu-22.04, fabric, 3.11, 2.1)	6m 5s
fabric-cpu (windows-2022, fabric, 3.11, 2.1)	6m 9s
fabric-cpu (macOS-11, lightning, 3.8, 1.12, oldest)	7m 36s
fabric-cpu (ubuntu-20.04, lightning, 3.8, 1.12, oldest)	6m 7s
fabric-cpu (windows-2022, lightning, 3.8, 1.12, oldest)	7m 56s
fabric-cpu (macOS-11, fabric, 3.8, 1.13)	5m 54s
fabric-cpu (ubuntu-20.04, fabric, 3.8, 1.13)	5m 13s
fabric-cpu (windows-2022, fabric, 3.8, 1.13)	5m 23s
	2h 30m 57s

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