Added proper destruction of new objects recently added to
the context (VerterArray, Sampler and TransformFeedback).

Change-Id: I45a741476d84b74469d5463653eb6a3bb04d501d
Reviewed-on: https://swiftshader-review.googlesource.com/2813Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>