For Grasshopper OMAC_ACPKM, OMAC and MAGMA, support XOF

XOF (eXtendable-Output Function) is supported in OpenSSL since version
1.1.1.  Unfortunately, that support is limited, as it requires calling
EVP_DigestFinalXOF().  However, the grasshopper code wasn't compatible.

This changeset adds XOF support in grasshopper

This changeset removes the _meth_ calls from test_grasshopper.c (they
should never have been there, but considering support for XOF came so
late in OpenSSL, their presence is understandable) and uses supported
functionality for this sort of thing instead.