lib/tss2/tss2_structs.h: Fix clang build - remove duplicate typedef

lib/tss2/tss2_structs.h: Fix clang build - remove duplicate typedef

grub-core/lib/tss2/tss2_structs.h contains a duplicate typedef as follows:
  typedef TPMS_SCHEME_HASH_t TPMS_SCHEME_KDF2_t;

This causes a build failure when compiling with clang. Remove the
duplicate typedef which allows successfully building GRUB with clang.

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>
Reviewed-by: Gary Lin <glin@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>