x86: remove offsets.h from .gitignore and dontdiff

Commit 77d1a499 ("x86, boot: make
symbols from the main vmlinux available") removed all traces of
offsets.h from the tree. Remove its entries in dontdiff and x86/boot's
.gitignore file too.
Signed-off-by: NPaul Bolle <pebolle@tiscali.nl>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Documentation/dontdiff

@@ -181,7 +181,6 @@ modversions.h*
 nconf
 ncscope.*
 offset.h
-offsets.h
 oui.c*
 page-types
 parse.c

arch/x86/boot/.gitignore

@@ -2,7 +2,6 @@ bootsect
 bzImage
 cpustr.h
 mkcpustr
-offsets.h
 voffset.h
 zoffset.h
 setup