Remove metadata tests for features that are not implemented
Remove metadata tests for features that are not implemented

The metadata tests depend on the corresponding feature because there
is no guarantee that the metadata is correct if the feature is
disabled. There are metadata test cases for some algorithms and key
types that are declared but not supported. These test cases are
present but can never run.

It is debatable whether having these test cases is a good thing in
case they become runnable in the future, or a bad thing because
they're dead code. We're working on detecting test cases that are
never executed for accidental reasons (e.g. typo in a dependency or
missing configuration on the CI), and having test cases that are
deliberately never executed messes this up. So remove these test
cases. If we do implement the corresponding feature, it'll be easy to
add the corresponding metadata test cases.

The features that had metadata tests but no implementations were:

* SHA-512/256 and SHA-512/224 (hypothetical dependency: MBEDTLS_SHA512_256)
* DSA (hypothetical dependency: MBEDTLS_DSA_C)
* SHA-3 and HMAC-SHA-3 (hypothetical dependency: MBEDTLS_SHA3_C)

Signed-off-by: Gilles Peskine <f805f64266d288fc5467baa7be6cd0ff366f477b@arm.com>

ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls