Patternfly react 4 removes the clear button when no onClear callback is passed as prop. This css class is no longer needed https://github.com/3scale/porta/blob/0b2cb7c423e42201a11f2274c16749a03977d43a/app/javascript/src/Common/components/Select.scss#L1

Do the same in our Select, remove isClearable in favor of an optional onClear callback: https://github.com/3scale/porta/blob/ffd640fefe1a3e8589a4f494a20e7006756ab4bb/app/javascript/src/Common/components/Select.tsx#L89