Remove version range upper bound

Since students were experiencing problems whenever they updated their IDEs due to an upper bound in the plugin configuration, I decided to just remove it entirely. It does not appear to be possible to set a restriction to the major version, like 2024.*. Therefore, this change makes sense. This does mean that, whenever breaking changes in the PSI/whatever API occur, the plugin might not work properly, but this should be good enough. This event is quite unlikely and if it does happen, the plugin would not have worked before this change in the first place.

I noticed that the docs talk about this, and apparently it is perfectly legal to omit the until-build property, as demonstrated by one of the examples in the docs:

<!-- 2021.3.3 or later -->
<idea-version since-build="213.7172.25"/>