Merge EventSub.{ReadAll|ReadPast|ReadFuture} into Read

[ggwpez]

Location: [backend/ethc/channel/subscription]

Task: Instead of having three different read functions: ReadAll, ReadPast and ReadFuture we only want to have a single Read function.
This simplifies the event sub code a lot and the cases that the other functions cover are not needed right now.

[ggwpez]

The idea of removing ReadPast works in theory, but after doing so all of our Funder and Adjudicator tests needed to be adjusted.
The tests also needed 33 instead of the current 6 seconds. I think it is therefore better to just remove ReadFuture and rename ReadAll to Read for now.

We only need the ReadPast function in one location that we wanted to revise anyway so fixing all tests is not worth the effort IMHO.
@matthiasgeihs

[matthiasgeihs]

OK, thanks for looking into it. I am fine with taking your suggested approach (i.e., keep ReadPast for now). In the long term, I think we should still consider replacing ReadPast with Read.