Stop the special treatment of invalid hashAlgorithm of the message
imprint. Those invalid values can only appear after the object is
instantiated, before the user sets an actual message digest algorithm.
OpenSSL::Timestamp::TokenInfo#algorithm already does the same.
Also, remove the test case "test_create_request" since it does not make
much sense. Those fields are to be set by the user after creation of
the object and checking the initial value is pointless.
Fixes: https://github.com/ruby/openssl/issues/335https://github.com/ruby/openssl/commit/890a6476fa