scsi: aic7xxx: Remove more FreeBSD-specific code

Remove additional code for FreeBSD in aic7xxx_core.c, which is unneeded
since commit cca6cb8a ("scsi: aic7xxx: Fix build using bare-metal
toolchain").

Link: https://lore.kernel.org/r/20200327191102.78554-1-alex.dewar@gmx.co.uk


Suggested-by: Martin Petersen <martin.petersen@oracle.com>
Signed-off-by: Alex Dewar <alex.dewar@gmx.co.uk>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>