remove deprecated buffer.get/.set methods

remove deprecated buffer.get/.set methods

Node.js commit:
https://github.com/nodejs/node/commit/101bca988cebce584d5b6098c316a6e7bf
89b69d

These have been deprecated since Apr 27, 2013, and the plan was to
remove them in "node v0.13".

buffer.get(index) is superseded by buffer[index].
buffer.set(index, value) is superseded by buffer[index] = value.

These have never been documented at any point in node's history.