Remove 2.3 example from pull request template

Mentioning 2.3 here is going to be anachronistic when 2.4 exists. And
there's not really any point in bumping this version number every time
the game's version number is bumped as well. So it's best to just remove
it.

.github/pull_request_template.md

@@ -29,8 +29,7 @@ Describe your patch here!
 
 By submitting this pull request, I confirm that...
 
-- [ ] My changes may be used in a future commercial release of VVVVVV (for
-  example, a 2.3 update on Steam for Windows/macOS/Linux)
+- [ ] My changes may be used in a future commercial release of VVVVVV
 - [ ] I will be credited in a `CONTRIBUTORS` file and the "GitHub Friends"
   section of the credits for all of said releases, but will NOT be compensated
   for these changes