Rework RemoveLog service

* Add Instrumentation and specs
* When expectations are not met, return a Hash with some information
for consumers to use
[WIP] Add removed_at and removed_by to Log
Do not check log content in instrumentation spec

It seems rather awkward to work out a stub that matches
the log with removed, so that the spec passes.
The log contents are tested in other places in this spec file.
Raise errors if log cannot be removed

Avoid using a Hash to pass error conditions while removing logs.
Use descriptive variable name for log removal timestamp