Relax some dependencies

- DTLS_HELLO_VERIFY no longer depends on SRV_C
- SSL_COOKIE_C no longer depends on DTLS_HELLO_VERIFY

Not that much work for us, and easier on users (esp. since it allows just
disabling SRV_C alone).
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index aef4dfb..6cd46e8 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1087,8 +1087,7 @@
  *
  * \warning Disabling this can ba a security risk! (see above)
  *
- * Requires: MBEDTLS_SSL_SRV_C
- *           MBEDTLS_SSL_PROTO_DTLS
+ * Requires: MBEDTLS_SSL_PROTO_DTLS
  *
  * Comment this to disable support for HelloVerifyRequest.
  */
@@ -2085,8 +2084,6 @@
  *
  * Module:  library/ssl_cookie.c
  * Caller:
- *
- * Requires: MBEDTLS_SSL_DTLS_HELLO_VERIFY
  */
 #define MBEDTLS_SSL_COOKIE_C