Remove stli(4). Also remove ISA support from stl(4).

Remove stli(4). Also remove ISA support from stl(4).

stli(4) was ISA only. stl(4) was for ISA/PCI controllers.

The stlload(8) and stlstty(8) utilities were for ISA controllers only,
so remove them too (along with ISA only firmware).

While here, clean up stl(4) a bit.

• [DBH] Makefile_upgrade.inc
• [DBH] UPDATING
• [DBH] etc/mtree/BSD.usr.dist
• [DBH] share/man/man4/isa.4
• [DBH] share/man/man4/man4.i386/Makefile
• [DBH] share/man/man4/man4.i386/stl.4
• [DBH] share/man/man7/hier.7
• [DBH] sys/bus/isa/i386/isa_compat.h
• [DBH] sys/config/LINT
• [DBH] sys/dev/serial/stl/stallion.c
• [DBH] sys/dev/serial/stli/istallion.c
• [DBH] sys/platform/pc32/conf/files
• [DBH] sys/platform/pc32/i386/userconfig.c
• [DBH] sys/platform/pc32/isa/README.stl
• [DBH] usr.sbin/stallion/Makefile
• [DBH] usr.sbin/stallion/Makefile.inc
• [DBH] usr.sbin/stallion/bootcode/2681.sys.uu
• [DBH] usr.sbin/stallion/bootcode/Makefile
• [DBH] usr.sbin/stallion/bootcode/cdk.sys.uu
• [DBH] usr.sbin/stallion/stlload/Makefile
• [DBH] usr.sbin/stallion/stlload/stlload.8
• [DBH] usr.sbin/stallion/stlload/stlload.c
• [DBH] usr.sbin/stallion/stlstats/stlstats.8
• [DBH] usr.sbin/stallion/stlstty/Makefile
• [DBH] usr.sbin/stallion/stlstty/stlstty.8
• [DBH] usr.sbin/stallion/stlstty/stlstty.c