Remove last traces of ikconfig.h

The build system stopped generating ikconfig.h in v2.6.8. Remove an entry
for it in dontdiff. There's also a reference to it in a small comment.
Remove that comment too, as it is of little help in any case.
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/dontdiff

@@ -139,7 +139,6 @@ hpet_example
 hugepage-mmap
 hugepage-shm
 ihex2fw
-ikconfig.h*
 inat-tables.c
 initramfs_list
 int16.c

kernel/Makefile

@@ -115,8 +115,6 @@ obj-$(CONFIG_HAS_IOMEM) += memremap.o
 
 $(obj)/configs.o: $(obj)/config_data.h
 
-# config_data.h contains the same information as ikconfig.h but gzipped.
-# Info from config_data can be extracted from /proc/config*
 targets += config_data.gz
 $(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
 	$(call if_changed,gzip)