chore($sniffer): Remove $sniffer.hashchange

The hashchange event is not supported only in ancient browsers like Android<2.2
and IE<8. Angular never really supported IE7 and in 1.3 where support for IE8
is dropped it makes even less sense to check for hashchange support.
Yes. @realityking suggested more code can be removed, referring to `$browser.addPollFn`. I noted that it's still used in `ngCookies` co cannot be removed; @IgorMinar said it can be moved to `ngCookies` but not now.