crypto: Move declaration of crypto_init_siphash_key() into crypto.h.

On second thought, this is a global initialisation function and
doesn't conceptually have much to do with getting/using randomnesses.

src/common/crypto.h

@@ -38,6 +38,7 @@ typedef struct aes_cnt_cipher crypto_cipher_t;
 typedef struct crypto_dh_t crypto_dh_t;
 
 /* global state */
+int crypto_init_siphash_key(void);
 int crypto_early_init(void) ATTR_WUR;
 int crypto_global_init(int hardwareAccel,
                        const char *accelName,

src/common/crypto_rand.h

@@ -29,7 +29,6 @@ uint64_t crypto_rand_uint64(uint64_t max);
 double crypto_rand_double(void);
 struct tor_weak_rng_t;
 void crypto_seed_weak_rng(struct tor_weak_rng_t *rng);
-int crypto_init_siphash_key(void);
 
 char *crypto_random_hostname(int min_rand_len, int max_rand_len,
                              const char *prefix, const char *suffix);