This comes from MDL-73500, where a number of php < 73 checks were removed from core because they contained deprecated / removed functionality in php 80.

There, it was detected that we still have a good number of old checks in code (some dating back to php 5x).

And, all them, are 100% unnecessary/unreachable code tight now, because Moodle 3.11 (and up) requires php 73. And surely Moodle 4.1 will require php 74.

So this issue is about to remove all those checks and the branches of code being executed for those old php versions.

Note this does not apply to 3rd part libraries.

Ciao