[optimise] Remove unnecessary code in Adam.
[optimise] Remove unnecessary code in Adam.

This commit removes the public theta field in the Java
implementation of AdamOptimizer. It is no longer necessary
because cortex.optimise/Adam saves the parameter vector in its
:parameters field and returns it when the parameters protocol
method is called. (The Java implementation mutates the underlying
double array, so returning the same core.matrix vector is fine.)

thinktopic/cortex,thinktopic/cortex,thinktopic/cortex,thinktopic/cortex