upstream: Remove now-unused compat bit SSH_BUG_BIGENDIANAES. This

was previously set for OpenSSH 2.3 (released in 2000) but this check was
removed in OpenSSH 7.7 (2018).  ok djm@ deraadt@

OpenBSD-Commit-ID: 326426ea328707fc9e83305291ab135c87f678af
