secp224k1 is the one with 225-bit private keys.
The consequences of this mistake were:
* We emitted positive test cases for hypothetical SECP_R1_225 and
SECP_K1_224 curves, which were never executed.
* We emitted useless not-supported test cases for SECP_R1_225 and SECP_K1_224.
* We were missing positive test cases for SECP_R1_224 in automatically
generated tests.
* We were missing not-supported test cases for SECP_R1_224 and SECP_K1_225.
Thus this didn't cause test failures, but it caused missing test coverage
and some never-executed test cases.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>