rename changeGitConfig to overrideGitConfig and avoid unncessary calls

It's important that it be clear that it overrides a config, such that
reloading the git config won't change it, and in particular, setConfig
won't change it.

Most of the calls to changeGitConfig were actually after setConfig,
which was redundant and unncessary. So removed those.

The only remaining one, besides --debug, is in the handling of
repository-global config values. That one's ok, because the
way mergeGitConfig is implemented, it does not override any value that
is set in git config. If a value with a repo-global setting was passed
to setConfig, it would set it in the git config, reload the git config,
re-apply mergeGitConfig, and use the newly set value, which is the right
thing.

Upgrade/V5.hs

@@ -10,7 +10,6 @@
 module Upgrade.V5 where
 
 import Annex.Common
-import qualified Annex
 import Config
 import Config.Smudge
 import Annex.InodeSentinal
@@ -84,7 +83,6 @@ convertDirect = do
 	 - space, with less preservation of old versions of files
 	 - as does annex.thin. -}
 	setConfig (annexConfig "thin") (boolConfig True)
-	Annex.changeGitConfig $ \c -> c { annexThin = True }
 	Direct.setIndirect
 	cur <- fromMaybe (error "Somehow no branch is checked out")
 		<$> inRepo Git.Branch.current

Upgrade/V5/Direct.hs

@@ -19,7 +19,6 @@ module Upgrade.V5.Direct (
 ) where
 
 import Annex.Common
-import qualified Annex
 import qualified Git
 import qualified Git.Config
 import qualified Git.Ref
@@ -35,7 +34,6 @@ setIndirect = do
 	setbare
 	switchHEADBack
 	setConfig (annexConfig "direct") val
-	Annex.changeGitConfig $ \c -> c { annexDirect = False }
   where
 	val = Git.Config.boolConfig False
 	coreworktree = ConfigKey "core.worktree"