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.

Messages/Progress.hs

@@ -5,8 +5,6 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
-{-# LANGUAGE CPP #-}
-
 module Messages.Progress where
 
 import Common
@@ -16,12 +14,10 @@ import Types
 import Types.Messages
 import Types.Key
 import qualified Messages.JSON as JSON
-
-#ifdef WITH_CONCURRENTOUTPUT
 import Messages.Concurrent
+
 import qualified System.Console.Regions as Regions
 import qualified System.Console.Concurrent as Console
-#endif
 
 {- Shows a progress meter while performing a transfer of a key.
  - The action is passed the meter and a callback to use to update the meter.
@@ -45,7 +41,6 @@ metered othermeter key getsrcfile a = withMessageState $ \st ->
 		liftIO $ clearMeterHandle meter stdout
 		return r
 	go msize (MessageState { outputType = NormalOutput, concurrentOutputEnabled = True }) =
-#if WITH_CONCURRENTOUTPUT
 		withProgressRegion $ \r -> do
 			meter <- liftIO $ mkMeter msize $ \_ msize' old new ->
 				let s = bandwidthMeter msize' old new
@@ -53,9 +48,6 @@ metered othermeter key getsrcfile a = withMessageState $ \st ->
 			m <- liftIO $ rateLimitMeterUpdate 0.2 meter $
 				updateMeter meter
 			a meter (combinemeter m)
-#else
-		nometer
-#endif
 	go msize (MessageState { outputType = JSONOutput jsonoptions })
 		| jsonProgress jsonoptions = do
 			buf <- withMessageState $ return . jsonBuffer
@@ -133,7 +125,6 @@ mkStderrRelayer = do
 mkStderrEmitter :: Annex (String -> IO ())
 mkStderrEmitter = withMessageState go
   where
-#ifdef WITH_CONCURRENTOUTPUT
-	go s | concurrentOutputEnabled s = return Console.errorConcurrent
-#endif
-	go _ = return (hPutStrLn stderr)
+	go s
+		| concurrentOutputEnabled s = return Console.errorConcurrent
+		| otherwise = return (hPutStrLn stderr)