make login more sturdy

src/elm/services/UserService.py

@@ -1,4 +1,3 @@
-from asyncio import sleep
 from hashlib import sha256
 from typing import Optional
 from string import ascii_letters, digits
@@ -69,8 +68,6 @@ class UserService:
 
     async def is_login_valid(self, user_name: str, password_clear_text: str) -> bool:
         user = await self.get_user(user_name)
-        if not user:
-            user = await self.get_user(user_name.lower())  # Migrated users had all lowercase names
         user_password_hash = sha256(password_clear_text.encode(encoding="utf-8")).hexdigest()
         if not user:
             return False