Remove reference to ECJPAKE

Remove reference to `MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED` as branch
`mbedtls-2.1` doesn't have `ECJPAKE`. This definition was accidently
inserted in a backport.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 4701b13..14b7a48 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -678,8 +678,7 @@
     unsigned char offer_compress;
     const int *ciphersuites;
     const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
-#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
-    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
     int uses_ec = 0;
 #endif
 
@@ -833,8 +832,7 @@
         MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %2d",
                        ciphersuites[i] ) );
 
-#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
-    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
         uses_ec |= mbedtls_ssl_ciphersuite_uses_ec( ciphersuite_info );
 #endif