Remove default support of OLD TLV and JSON code

[sbernard31]

Leshan support old TLV and JSON code. This old code was used by the past because official code was not yet declared to iana.

The LWM2M specification is out since a February 2017 and old code should not be used anymore.
So this PR deactivate the support of those codes be default, but this is still possible to activate it like this :

LeshanServerBuilder builder = new LeshanServerBuilder();
builder.setEncoder(new DefaultLwM2mNodeEncoder(true));