user deletions: fix rename conflict logic.

Remove the 10-try limit when there's a name conflict during renaming. We
forgot to increment the loop counter so this did nothing. This wasn't
necessary anyway since the loop will always terminate eventually because
names have finite length.

app/logical/user_deletion.rb

@@ -50,12 +50,7 @@ class UserDeletion
 
   def rename
     name = "user_#{user.id}"
-    n = 0
-    name += "~" while User.where(:name => name).exists? && (n < 10)
-
-    if n == 10
-      raise ValidationError.new("New name could not be found")
-    end
+    name += "~" while User.exists?(name: name)
 
     request = UserNameChangeRequest.new(user: user, desired_name: name, original_name: user.name)
     request.save!(validate: false) # XXX don't validate so that the 1 name change per week rule doesn't interfere