[secp256k1] Remove old `libsecp256k1_fail_on_bad_count` features #5241

Job	Run time
android (ubuntu-20.04, x86_64-linux-android)	2m 46s
android (ubuntu-20.04, aarch64-linux-android)	3m 1s
android (ubuntu-20.04, i686-linux-android)	2m 51s
ios (macos-12, aarch64-apple-ios)	3m 42s
android (ubuntu-20.04, armv7-linux-androideabi)	3m 6s
ios (macos-12, x86_64-apple-ios)	3m 49s
ios (macos-12, aarch64-apple-darwin)	4m 3s
ios (macos-12, x86_64-apple-darwin)	3m 31s
error_reporting	0s
	26m 49s

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