crypto/secp256k1: update to github.com/bitcoin-core/secp256k1 @ 9d560f9 (#3544)

- Use defined constants instead of hard-coding their integer value.
- Allocate secp256k1 structs on the C stack instead of converting []byte
- Remove dead code

crypto/secp256k1/libsecp256k1/src/util.h

@@ -57,7 +57,10 @@ static SECP256K1_INLINE void secp256k1_callback_call(const secp256k1_callback *
 #endif
 
 /* Like assert(), but when VERIFY is defined, and side-effect safe. */
-#ifdef VERIFY
+#if defined(COVERAGE)
+#define VERIFY_CHECK(check)
+#define VERIFY_SETUP(stmt)
+#elif defined(VERIFY)
 #define VERIFY_CHECK CHECK
 #define VERIFY_SETUP(stmt) do { stmt; } while(0)
 #else