Revert "IRConnection : modify register(), login()"

[zkldi]

This reverts commit 3c0c1feca2df5a0d5d1dc5c3dc0be580ee39e6c8.

Why

This change breaks every existing IR and does absolutely nothing else. IRAccount is not used anywhere else, and has no different functionality.

With this change, all IRs now have to distribute two versions of their code, as people will be on <0.8.6 for a long time.

It would be much more convenient for IRs to not have to distribute multiple versions of their .jar files.

[seraxis]

Seconding this, a huge breaking change like this requires justification

これに賛成だ。このような重要な変更には、正当な理由が必要と思います

[zkldi]

I didn't realise 0.8.6 was released. There's no point fixing this now. We'll deal with the downstream breakage.