clean up url removal presence update

* rmurl: Fix a case where removing the last url left git-annex thinking
  content was still present in the web special remote.
* SETURLPRESENT, SETURIPRESENT, SETURLMISSING, and SETURIMISSING
  used to update the presence information of the external special remote
  that called them; this was not documented behavior and is no longer done.

Done by making setUrlPresent and setUrlMissing only update presence info
for the web, and only when the url is a web url. See the comment for
reasoning about why that's the right thing to do.

In AddUrl, had to make it update location tracking, to handle the
non-web-url case.

This commit was sponsored by Ewen McNeill on Patreon.

Command/RmUrl.hs

@@ -49,5 +49,5 @@ start (file, url) = flip whenAnnexed file $ \_ key -> do
 cleanup :: String -> Key -> CommandCleanup
 cleanup url key = do
 	r <- Remote.claimingUrl url
-	setUrlMissing (Remote.uuid r) key (setDownloader' url r)
+	setUrlMissing key (setDownloader' url r)
 	return True