Remove unnecessary guards in client-side EC curve extension writing

ssl_write_supported_elliptic_curves_ext() is guarded by

```
    #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
       defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
```

each of which implies (by check_config.h) that MBEDTLS_ECP_C
is enabled.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index d45f3d3..d226e65 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -270,15 +270,9 @@
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported_elliptic_curves extension" ) );
 
-#if defined(MBEDTLS_ECP_C)
     for( grp_id = ssl->conf->curve_list; *grp_id != MBEDTLS_ECP_DP_NONE; grp_id++ )
-#else
-    for( info = mbedtls_ecp_curve_list(); info->grp_id != MBEDTLS_ECP_DP_NONE; info++ )
-#endif
     {
-#if defined(MBEDTLS_ECP_C)
         info = mbedtls_ecp_curve_info_from_grp_id( *grp_id );
-#endif
         if( info == NULL )
         {
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid curve in ssl configuration" ) );
@@ -296,15 +290,9 @@
 
     elliptic_curve_len = 0;
 
-#if defined(MBEDTLS_ECP_C)
     for( grp_id = ssl->conf->curve_list; *grp_id != MBEDTLS_ECP_DP_NONE; grp_id++ )
-#else
-    for( info = mbedtls_ecp_curve_list(); info->grp_id != MBEDTLS_ECP_DP_NONE; info++ )
-#endif
     {
-#if defined(MBEDTLS_ECP_C)
         info = mbedtls_ecp_curve_info_from_grp_id( *grp_id );
-#endif
         elliptic_curve_list[elliptic_curve_len++] = info->tls_id >> 8;
         elliptic_curve_list[elliptic_curve_len++] = info->tls_id & 0xFF;
     }