Remove Actions Utility Methods

[benjchristensen]

Related to #1797 it looks like we should remove the following unused methods in Actions:

    public static <T> Action1<T> onNextFrom(final Observer<T> observer) {
    public static <T> Action1<Throwable> onErrorFrom(final Observer<T> observer) {
    public static <T> Action1<T> onNextFrom(final Observer<T> observer) {

[akarnokd]

I added them to support the join patterns but only onErrorFrom was ever used. They can be deleted from core but onErrorFrom needs to be moved over and actualized in Plan1...PlanN.