Fix instructions and test data for pyhsslms interop tests
Fix instructions and test data for pyhsslms interop tests

The test data was invalid because it had the extra 4-byte prefix for HSS.
Regenerate it (which produces completely new signatures since it is
randomized).

Rearrange the reproduction instructions for the second test case so that it
shows more clearly how to generate a second signature with the same private
key.

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

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