Make git-annex enable-tor work when using the linux standalone build

Clean the standalone environment before running the su command
to run "sh". Otherwise, PATH leaked through, causing it to run
git-annex.linux/bin/sh, but GIT_ANNEX_DIR was not set,
which caused that script to not work:

[2022-10-26 15:07:02.145466106] (Utility.Process) process [938146] call: pkexec ["sh","-c","cd '/home/joey/tmp/git-annex.linux/r' && '/home/joey/tmp/git-annex.linux/git-annex' 'enable-tor' '1000'"]
/home/joey/tmp/git-annex.linux/bin/sh: 4: exec: /exe/sh: not found

Changed programPath to not use GIT_ANNEX_PROGRAMPATH,
but instead run the scripts at the top of GIT_ANNEX_DIR.
That works both when the standalone environment is set up, and when it's
not.

Sponsored-by: Kevin Mueller on Patreon

Assistant/Install.hs

@@ -171,25 +171,3 @@ installFileManagerHooks program = unlessM osAndroid $ do
 #else
 installFileManagerHooks _ = noop
 #endif
-
-{- Returns a cleaned up environment that lacks settings used to make the
- - standalone builds use their bundled libraries and programs.
- - Useful when calling programs not included in the standalone builds.
- -
- - For a non-standalone build, returns Nothing.
- -}
-cleanEnvironment :: IO (Maybe [(String, String)])
-cleanEnvironment = clean <$> getEnvironment
-  where
-	clean environ
-		| null vars = Nothing
-		| otherwise = Just $ catMaybes $ map (restoreorig environ) environ
-	  where
-		vars = words $ fromMaybe "" $
-			lookup "GIT_ANNEX_STANDLONE_ENV" environ
-		restoreorig oldenviron p@(k, _v)
-			| k `elem` vars = case lookup ("ORIG_" ++ k) oldenviron of
-				(Just v')
-					| not (null v') -> Just (k, v')
-				_ -> Nothing
-			| otherwise = Just p