cms: remove `pem` feature #900

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	28s
minimal-versions	0s
build (1.81.0, wasm32-unknown-unknown)	25s
build (stable, thumbv7em-none-eabi)	19s
build (stable, wasm32-unknown-unknown)	29s
test (1.81.0)	27s
test (stable)	22s
	2m 30s

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