create-diff-object: do not strip STN_UNDEF symbols from *.fixup

create-diff-object: do not strip STN_UNDEF symbols from *.fixup

The rela groups in the *.fixup sections vary in size. That makes it
more complex to handle in the livepatch_strip_undefined_elements().
It is also unnecessary as the .fixup sections are unlikely to have
any STN_UNDEF symbols anyway.

Signed-off-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>