removed the old Android app

Running git-annex linux builds in termux seems to work well enough that the
only reason to keep the Android app would be to support Android 4-5, which
the old Android app supported, and which I don't know if the termux method
works on (although I see no reason why it would not).
According to [1], Android 4-5 remains on around 29% of devices, down from
51% one year ago.

[1] https://www.statista.com/statistics/271774/share-of-android-platforms-on-mobile-devices-with-android-os/

This is a rather large commit, but mostly very straightfoward removal of
android ifdefs and patches and associated cruft.

Also, removed support for building with very old ghc < 8.0.1, and with
yesod < 1.4.3, and without concurrent-output, which were only being used
by the cross build.

Some documentation specific to the Android app (screenshots etc) needs
to be updated still.

This commit was sponsored by Brett Eisenberg on Patreon.

Command/WebApp.hs

@@ -19,9 +19,6 @@ import Assistant.Install
 import Annex.Environment
 import Utility.WebApp
 import Utility.Daemon (checkDaemon)
-#ifdef __ANDROID__
-import Utility.Env
-#endif
 import Utility.UserInfo
 import Annex.Init
 import qualified Git
@@ -188,18 +185,7 @@ firstRun o = do
 			Annex.eval state $
 				startDaemon True True Nothing Nothing (listenAddress o) $ Just $
 					sendurlback v
-	sendurlback v _origout _origerr url _htmlshim = do
-		recordUrl url
-		putMVar v url
-
-recordUrl :: String -> IO ()
-#ifdef __ANDROID__
-{- The Android app has a menu item that opens the url recorded
- - in this file. -}
-recordUrl url = writeFile "/sdcard/git-annex.home/.git-annex-url" url
-#else
-recordUrl _ = noop
-#endif
+	sendurlback v _origout _origerr url _htmlshim = putMVar v url
 
 openBrowser :: Maybe FilePath -> FilePath -> String -> Maybe Handle -> Maybe Handle -> IO ()
 openBrowser mcmd htmlshim realurl outh errh = do
@@ -207,7 +193,6 @@ openBrowser mcmd htmlshim realurl outh errh = do
 	openBrowser' mcmd htmlshim' realurl outh errh
 
 openBrowser' :: Maybe FilePath -> FilePath -> String -> Maybe Handle -> Maybe Handle -> IO ()
-#ifndef __ANDROID__
 openBrowser' mcmd htmlshim realurl outh errh =
 	ifM osAndroid
 		{- Android does not support file:// urls well, but neither
@@ -216,20 +201,6 @@ openBrowser' mcmd htmlshim realurl outh errh =
 		( runbrowser realurl
 		, runbrowser (fileUrl htmlshim)
 		)
-#else
-openBrowser' mcmd htmlshim realurl outh errh = do
-	recordUrl realurl
-	{- Android's `am` command does not work reliably across the
-	 - wide range of Android devices. Intead, FIFO should be set to 
-	 - the filename of a fifo that we can write the URL to. -}
-	v <- getEnv "FIFO"
-	case v of
-		Nothing -> runbrowser realurl
-		Just f -> void $ forkIO $ do
-			fd <- openFd f WriteOnly Nothing defaultFileFlags
-			void $ fdWrite fd realurl
-			closeFd fd
-#endif
   where
 	runbrowser url = do
 		let p = case mcmd of