cms: remove `pem` feature (#1563) #1080

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	25s
test (1.81.0)	23s
build (1.81.0, wasm32-unknown-unknown)	26s
build (stable, thumbv7em-none-eabi)	19s
test (stable)	27s
build (stable, wasm32-unknown-unknown)	17s
minimal-versions	0s
	2m 17s

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