Clean duplicate aliases when creating from performer tagger

[WithoutPants]

Fixes #4596

[Maista6969]

Could you make this case insenstive? Stash-boxes allow Performer A to have both "Alias A" and "alias A" but local Stash will not

[Maista6969]

Actually since performers can be created through the Tagger view (original bug used Batch Add Performers as an example) this might need to be done on the back end