Convert to sdk/system/events
Convert to sdk/system/events

Simplify intercepting the "http-on-modify-request" event by using the
sdk provided system/events module rather than directly registering with
the observer-service. We are still using low level APIs that will
generate a warning from the linter, but the code is nicer looking.

wikimedia/FirefoxWikimediaDebug,wikimedia/FirefoxWikimediaDebug