OsPath build flag no longer depends on filepath-bytestring

However, filepath-bytestring is still in Setup-Depends.
That's because Utility.OsPath uses it when not built with OsPath.
It would be maybe possible to make Utility.OsPath fall back to using
filepath, and eliminate that dependency too, but it would mean either
wrapping all of System.FilePath's functions, or using `type OsPath = FilePath`

Annex.Import uses ifdefs to avoid converting back to FilePath when not
on windows. On windows it's a bit slower due to that conversion.
Utility.Path.Windows.convertToWindowsNativeNamespace got a bit
slower too, but not really worth optimising I think.

Note that importing Utility.FileSystemEncoding at the same time as
System.Posix.ByteString will result in conflicting definitions for
RawFilePath. filepath-bytestring avoids that by importing RawFilePath
from System.Posix.ByteString, but that's not possible in
Utility.FileSystemEncoding, since Setup-Depends does not include unix.
This turned out not to affect any code in git-annex though.

Sponsored-by: Leon Schuermann

Types/GitConfig.hs

@@ -64,7 +64,6 @@ import Control.Concurrent.STM
 import qualified Data.Set as S
 import qualified Data.Map as M
 import qualified Data.ByteString as B
-import qualified System.FilePath.ByteString as P
 
 -- | A configurable value, that may not be fully determined yet because
 -- the global git config has not yet been loaded.
@@ -244,7 +243,7 @@ extractGitConfig configsource r = GitConfig
 	, annexPidLock = getbool (annexConfig "pidlock") False
 	, annexPidLockTimeout = Seconds $ fromMaybe 300 $
 		getmayberead (annexConfig "pidlocktimeout")
-	, annexDbDir = (\d -> toOsPath (toRawFilePath d P.</> fromUUID hereuuid))
+	, annexDbDir = (\d -> toOsPath d </> fromUUID hereuuid)
 		<$> getmaybe (annexConfig "dbdir")
 	, annexAddUnlocked = configurable Nothing $
 		fmap Just $ getmaybe (annexConfig "addunlocked")