Unnecessary and confusing use of _currentUser variable

[juampiq6]

Hi team,
[context] -> gotrue package -> gotrue_client.dart

I found out that the_currentUser variable was being assigned as a copy of what _currentSession.user is already storing. I find it confusing for it to be a copied value when non needed. Unless I'm missing something, but I couldnt find other usages in the code.

I'm making a PR to solve this simple confusion.

Hope it helps.
Cheers