crcsync: fix memory leak in tests.

crcsync: fix memory leak in tests.

/home/rusty/devel/cvs/ccan/ccan/crcsync/test/run-crash.c:==6923== 112 bytes in 1 blocks are definitely lost in loss record 2 of 3
==6923==    at 0x402BA7A: malloc (vg_replace_malloc.c:261)
==6923==    by 0x80492EE: crcblocks (run-crash.c:20)
==6923==    by 0x8049448: main (run-crash.c:62)
==6923== 2,217 (2,212 direct, 5 indirect) bytes in 1 blocks are definitely lost in loss record 3 of 3
==6923==    at 0x402BA7A: malloc (vg_replace_malloc.c:261)
==6923==    by 0x8048AA0: crc_context_new (crcsync.c:85)
==6923==    by 0x8049476: main (run-crash.c:64)

/home/rusty/devel/cvs/ccan/ccan/crcsync/test/run.c:==11793== 512 bytes in 1 blocks are definitely lost in loss record 1 of 2
==11793==    at 0x402A52B: calloc (vg_replace_malloc.c:462)
==11793==    by 0x8049A3F: main (run.c:128)
==11793== 512 bytes in 1 blocks are definitely lost in loss record 2 of 2
==11793==    at 0x402A52B: calloc (vg_replace_malloc.c:462)
==11793==    by 0x8049A57: main (run.c:129)

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