cms: remove `pem` feature (#1563) #1626

Job	Run time
build (1.70.0, thumbv7em-none-eabi)	30s
build (1.70.0, wasm32-unknown-unknown)	38s
test (1.70.0)	1m 32s
build (stable, thumbv7em-none-eabi)	26s
test (stable)	1m 20s
build (stable, wasm32-unknown-unknown)	25s
minimal-versions / minimal-versions	59s
	5m 50s

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