Remove vestigial 3DFS support code (re: f88f302c)

Support for the long-dead 3DFS userland versioning file system was
already removed from ksh93 (although I'd overlooked some minor
things), but libast still supported it. This removes that too.

src/lib/libast/include/fs3d.h,
src/lib/libast/man/fs3d.3,
src/lib/libast/misc/fs3d.c:
- Removed.

bin/package,
src/cmd/INIT/package.sh:
- Remove attempted use of removed vpath builtin.

src/cmd/ksh93/*:
- Remove minor 3dfs vestiges.

src/lib/lib{ast,cmd,coshell}/*:
- Remove code supporting 3dfs.

src/cmd/ksh93/Mamfile

@@ -232,10 +232,6 @@ meta FEATURE/dynamic features/%>FEATURE/% features/dynamic dynamic
 make features/dynamic
 done features/dynamic
 exec - iffe -v -c '${CC} ${mam_cc_FLAGS} ${CCFLAGS}   ${LDFLAGS} ' ref ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -I${PACKAGE_ast_INCLUDE} -I${INSTALLROOT}/include ${mam_libdll} ${mam_libcoshell} ${mam_libcmd} ${mam_libast} ${mam_libm} ${mam_libnsl} : run features/dynamic
-make ${PACKAGE_ast_INCLUDE}/fs3d.h implicit
-prev ${PACKAGE_ast_INCLUDE}/ast_fs.h implicit
-prev ${PACKAGE_ast_INCLUDE}/prototyped.h implicit
-done ${PACKAGE_ast_INCLUDE}/fs3d.h dontcare
 prev ${PACKAGE_ast_INCLUDE}/dlldefs.h implicit
 done FEATURE/dynamic dontcare generated
 make FEATURE/options implicit