Eliminate an unused macro.
Fix signal delivery for the iBCS2 binaries.  The iBCS2 sysvec uses
current FreeBSD signal trampoline, but does not specifies
sv_sigcode_base, since shared page is not mapped.  This results in the
zero %eip for the signal frame.  Fall back to calculating %eip as
offset from the psstrings when sv_sigcode_base is not initialized.

Reported by:	Rich Naill <rich@enterprisesystems.net>
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week