Fix GCC warning with strncpy

GCC 8.2.1 warns that: ‘strncpy’ specified bound depends on the length
of the source argument. The length of username and password is checked
beforehand anyways, so "strncpy(dst, src, strlen(src))" should be the
same as "strcpy(dst, src)".

socks5.c

@@ -113,9 +113,9 @@ static int s5_client_auth(int s, const char *username, const char *password,
             uint8_t plen = (uint8_t)strlen(password);
             upauth[0] = RFC1929_VER; // VER = 1
             upauth[1] = ulen; // ULEN
-            strncpy((char *)(upauth + 2), username, ulen); // UNAME
+            strcpy((char *)(upauth + 2), username); // UNAME
             upauth[2 + ulen] = plen; // PLEN
-            strncpy((char *)(upauth + 3 + ulen), password, plen); // PASSWD
+            strcpy((char *)(upauth + 3 + ulen), password); // PASSWD
             err = dill_bsend(s, (void *)upauth, 3 + ulen + plen, deadline);
             if(dill_slow(err)) return -1;
             uint8_t upauthr[2];