task: remove prefix in death entry if killer is creature

[tobiasehlert]

We have logic that calculates a summon, if the death starts with a or an.
Deaths are not starting with those prefixes anymore..

Therefore we need to align deaths to not have those prefixes added to the death entry.

Additionally the summon check needs to be adjusted, so that it also checks for lowercase of death.
This is likely to be the case as reported in #439, #344 and probably #341.

https://github.com/TibiaData/tibiadata-api-go/blob/086f48317cdeff4982c4d084d4121c240143d66b/src/TibiaCharactersCharacter.go#L783-L794