Legacy: Remove backward compat functions

Between v1.0.0-beta.8 and beta.9 we cleaned up code to make the header smaller. this change broke signature verification and header hashing. we added a legacy path to make this old path work. Once eden and other testnets are migrated off, we should remove this legacy code. 

There could be other places we have some extra legacy code, as we find it we should add it here to be removed later on