In 0.3.4 and later, these functions are declared in rephist.h:
STATIC uint64_t find_largest_max(bw_array_t *b);
STATIC void commit_max(bw_array_t *b);
STATIC void advance_obs(bw_array_t *b);

But in 0.2.9, they are declared in rephist.c and test_relay.c.

So compilers fail with a "must use 'struct' tag" error.

We add the missing struct typedef in test_relay.c, to match the
declarations in rephist.c.

(Merge commit 813019cc moves these functions into rephist.h instead.)

Fixes bug 30184; not in any released version of Tor.