Remove misleading and redundant guard around restartable ECC field

`MBEDTLS_SSL__ECP_RESTARTABLE` is only defined if
`MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED` is set, which
requires `MBEDTLS_X509_PARSE_C` to be set (this is checked
in `check_config.`). The additional `MBEDTLS_X509_PARSE_C`
guard around the `ecrs_peer_cert` field is therefore not
necessary; moreover, it's misleading, because it hasn't
been used consistently throughout the code.
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 5499115..0d543c1 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -331,9 +331,7 @@
         ssl_ecrs_cke_ecdh_calc_secret,  /*!< ClientKeyExchange: ECDH step 2 */
         ssl_ecrs_crt_vrfy_sign,         /*!< CertificateVerify: pk_sign()   */
     } ecrs_state;                       /*!< current (or last) operation    */
-#if defined(MBEDTLS_X509_CRT_PARSE_C)
     mbedtls_x509_crt *ecrs_peer_cert;        /*!< The peer's CRT chain.     */
-#endif /* MBEDTLS_X509_CRT_PARSE_C */
     size_t ecrs_n;                      /*!< place for saving a length      */
 #endif
 #if defined(MBEDTLS_X509_CRT_PARSE_C) && \