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.

Annex/GitOverlay.hs

@@ -14,6 +14,7 @@ import Git
 import Git.Types
 import Git.Index
 import Git.Env
+import Utility.Env
 import qualified Annex
 import qualified Annex.Queue
 
@@ -27,8 +28,8 @@ withIndexFile f a = do
 		a
   where
 	-- This is an optimisation. Since withIndexFile is run repeatedly,
-	-- and addGitEnv uses the slow copyGitEnv when gitEnv is Nothing, 
-	-- we cache the copied environment the first time, and reuse it in
+	-- and addGitEnv uses the slow getEnvironment when gitEnv is Nothing, 
+	-- we cache the environment the first time, and reuse it in
 	-- subsequent calls.
 	--
 	-- (This could be done at another level; eg when creating the
@@ -40,7 +41,7 @@ withIndexFile f a = do
 		Nothing -> do
 			e <- Annex.withState $ \s -> case Annex.cachedgitenv s of
 				Nothing -> do
-					e <- copyGitEnv
+					e <- getEnvironment
 					return (s { Annex.cachedgitenv = Just e }, e)
 				Just e -> return (s, e)
 			m (g { gitEnv = Just e })