elliptic-curve: leverage `CtOption::into_option` #1940

Job	Run time
build (1.60.0, thumbv7em-none-eabi)	1m 38s
minimal-versions	27s
build (1.60.0, wasm32-unknown-unknown)	1m 30s
test (1.60.0)	1m 34s
test (stable)	12s
build (stable, thumbv7em-none-eabi)	17s
build (stable, wasm32-unknown-unknown)	8s
	5m 46s

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