tinyCrypt: Remove check for Secp256r1 in SrvKeyExch writing

The use of tinyCrypt is restricted Secp256r1-only, and a check in
ssl_ciphersuite_is_match() ensures that an EC ciphersuite is chosen
only if the client advertised support for Secp256r1, too.
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 3198596..435588e 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3398,14 +3398,6 @@
                 0x04 /* Uncompressed */
             };
 
-            if( ssl->handshake->curve_tls_id != secp256r1_tls_id )
-            {
-                MBEDTLS_SSL_DEBUG_MSG( 1, ( "Unsupported curve %u (expected %u)",
-                                            (unsigned) ssl->handshake->curve_tls_id,
-                                            secp256r1_tls_id ) );
-                return( MBEDTLS_ERR_SSL_NO_CIPHER_CHOSEN );
-            }
-
             if( !uECC_make_key( ssl->handshake->ecdh_ownpubkey,
                                 ssl->handshake->ecdh_privkey,
                                 uecc_curve ) )