tlist: remove unused var warning in example.

Compiler:
/home/rusty/devel/cvs/ccan/ccan/tlist/tlist.h: In function ‘main’:
/home/rusty/devel/cvs/ccan/ccan/tlist/tlist.h:186:15: warning: variable ‘first’ set but not used [-Wunused-but-set-variable]

Compiler:
/home/rusty/devel/cvs/ccan/ccan/tlist/tlist.h: In function ‘main’:
/home/rusty/devel/cvs/ccan/ccan/tlist/tlist.h:205:15: warning: variable ‘last’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>