WiFiClientSecure: don't use the broken max_fragment_length extension (e…

…sp8266#4033)

axTLS does not correctly implement max_fragment_length extension. This
causes servers which understand this extension (currently GnuTLS- and
WolfSSL-based) to reject the client hello.

Until this is fixed in axTLS, remove the call to enable this extension
from WiFiClientSecure.

Fixes esp8266#3932.

libraries/ESP8266WiFi/src/WiFiClientSecure.cpp

@@ -113,7 +113,6 @@ class SSLContext
     {
         SSL_EXTENSIONS* ext = ssl_ext_new();
         ssl_ext_set_host_name(ext, hostName);
-        ssl_ext_set_max_fragment_size(ext, 4096);
         if (_ssl) {
             /* Creating a new TLS session on top of a new TCP connection.
                ssl_free will want to send a close notify alert, but the old TCP connection