Previously the code expected that there can be two references to the
same path max, because split editor is a toggle.
As @harawata pointed out[0], it is possible to have more than two
references to the same path because editor cloning can be done without
any limits.
This commit therefore removes the check for the reference list length.

[0] https://github.com/eclipse-platform/eclipse.platform.ui/issues/487#issuecomment-1357466836