doc: drop old ip command documentation

The old IP cross reference manual was very out of date, barely updated
since 1999.  The correct documentation is in the man pages.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

Makefile

@@ -73,7 +73,7 @@ install: all
 		$(DESTDIR)$(DOCDIR)/examples
 	install -m 0644 $(shell find examples/diffserv -maxdepth 1 -type f) \
 		$(DESTDIR)$(DOCDIR)/examples/diffserv
-	@for i in $(SUBDIRS) doc; do $(MAKE) -C $$i install; done
+	@for i in $(SUBDIRS);  do $(MAKE) -C $$i install; done
 	install -m 0644 $(shell find etc/iproute2 -maxdepth 1 -type f) $(DESTDIR)$(CONFDIR)
 	install -m 0755 -d $(DESTDIR)$(BASH_COMPDIR)
 	install -m 0644 bash-completion/tc $(DESTDIR)$(BASH_COMPDIR)
@@ -84,7 +84,7 @@ snapshot:
 		> include/SNAPSHOT.h
 
 clean:
-	@for i in $(SUBDIRS) doc; \
+	@for i in $(SUBDIRS); \
 	do $(MAKE) $(MFLAGS) -C $$i clean; done
 
 clobber: