Add SslCurve::to_nid() and remove SslCurveId #853

Job	Run time
rustfmt	12s
Test (stable)	2m 5s
clippy	3m 22s
Cross build from macOS to Linux (x86_64-unknown-linux-gnu)	1m 48s
Test (arm-android)	2m 2s
Test (arm64-android)	2m 7s
Cross build from macOS to Linux (FIPS) (x86_64-unknown-linux-gnu)	6m 38s
Test (i686-android)	2m 3s
Test features	6m 33s
Test FIPS integration	3m 13s
Test (x86_64-android)	2m 12s
Test (aarch64-ios)	2m 8s
Test (aarch64-ios-sim)	2m 13s
Test (x86_64-ios)	3m 36s
Test (i686-linux)	2m 21s
Test (arm-linux)	2m 13s
Test (aarch64-linux)	2m 21s
Test (arm64-macos)	2m 35s
Test (x86_64-macos)	2m 9s
Test (x86_64-mingw)	4m 30s
Test (i686-msvc)	5m 13s
Test (x86_64-msvc)	5m 26s
	1h 7m 0s

Provide feedback