Clean up HLT online messaging
At the time of initial implementation I thought it would be useful to have the extra information given by ATH_REPORT macros on warnings/errors, but in practice this turned out to be not such a good idea. The extra information isn't useful and only makes the messages longer and more difficult to read in large amount. This MR converts them all into the classic ATH_MSG macros.
In addition, also removing EventID printout from errors and warnings as this is now appended by TrigMessageSvc.