Provide correct documentation for `hedera-node/hapi-utils`

Consider hedera-node/hapi-utils. It contains a bunch of utility classes that I guess in some way are "hapi" utilities.

But the README.md doesn't describe them - or even the rule by which you'd find some utility class in this directory vs. some other (more specific?) directory.

In fact, the README.md is from a bygone era when this directory held the compiled protobufs from the protobuf repo. (I think.). And that also explains why there's this giant file HAPI.html describing the protobufs (and it's way out of date).

So this issue is:

1. Remove the existing README.md and HAPI.html - no longer applicable here.
2. Add a new README.md that properly describes the contents of this directory (and the decision rule you use to decide whether to place your own new utility class here, or somewhere else).

Start by inspecting hedera-node/hapi-utils/README.md and HAPI.html, then review the utility classes in that directory and nearby specific utility directories. Done means the obsolete README.md and HAPI.html are removed and a new README.md explains the directory contents and the rule for placing new utility classes here or elsewhere.