Remove some dead code in core/arrays/interval.py
The typing work both @twoertwein and I did in #46080 and #44922 found some code that I conjecture is dead code as it doesn't make sense from a typing perspective.

So this PR removes the dead code, which will then allow either of those PR's to get rid of some `#type : ignore` lines.

Not clear to me how to add tests for dead code removal.  In theory, all tests should pass when dead code is removed.


closing per comment above. Could use a test