Rollup merge of #119628 - RalfJung:duplicate-test, r=compiler-errors

remove duplicate test

This was added in ace6fc3 where overflowing-rsh-6 differed from overflowing-rsh-5 in a feature gate, but the feature has since been stabilized, making the tests 100% identical.

Most of these tests in numbers-arithmetic could be put into one file rather than having so many files that all test the same lint... but it doesn't seem worth the effort. After #119432 we might be able to remove most of them entirely as they will be covered by the new tests added there.

Author: compiler-errors