ios: drop deprecated MPS export step from both iOS scripts #4235

Job	Run time
test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job	19m 29s
test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job	25m 55s
test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job	23m 57s
test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job	17m 25s
test-arm / test-backend-macos	0s
test-arm / package-golden-artifacts	43s
	1h 27m 29s

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