kbuild: remove redundant line from (generic-)asm-offsets.h

This line produces an extra comment line for generic-asm-offsets.h
and asm-offsets.h.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
[ imported from Linux Kernel, commit 343d3e6cc861,
  with modification of commit description ]
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>