genksyms: Do not paste the bison header file to lex.c

The header is already #included, no need to include it a second time.
lex.c_shipped was regenerated using flex-2.5.35.

Signed-off-by: Michal Marek <mmarek@suse.cz>
Acked-by: Sam Ravnborg <sam@ravnborg.org>