Bug 1793463 - Part 6: Remove nsIProtocolHandler.{defaultPort,protocolFlags}, r=necko-reviewers,valentin

This removes all implementations of these types. Some implementations in JS
code were also removed in the previous part, when updating tests to use
`Services.io.registerProtocolHandler`.

Code which used to access these members should go through the IOService now
instead.

Differential Revision: https://phabricator.services.mozilla.com/D162805