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/AddUrl.hs

@@ -233,7 +233,8 @@ addUrlChecked o url file u checkexistssize key =
 			(exists, samesize, url') <- checkexistssize key
 			if exists && (samesize || relaxedOption (downloadOptions o))
 				then do
-					setUrlPresent u key url'
+					setUrlPresent key url'
+					logChange key u InfoPresent
 					next $ return True
 				else do
 					warning $ "while adding a new url to an already annexed file, " ++ if exists
@@ -397,7 +398,8 @@ addWorkTree u url file key mtmp = case mtmp of
   where
 	go = do
 		maybeShowJSON $ JSONChunk [("key", key2file key)]
-		setUrlPresent u key url
+		setUrlPresent key url
+		logChange key u InfoPresent
 		ifM (addAnnexedFile file key mtmp)
 			( do
 				when (isJust mtmp) $