Remove `--local`

`--local` isn't supported by versions of Git older than 1.8. But it
should be the default if the `--local` is omitted.

yadm

@@ -763,7 +763,7 @@ EOF
 
     # operate on the yadm repo's configuration file
     # this is always local to the machine
-    "$GIT_PROGRAM" config --local "$@"
+    "$GIT_PROGRAM" config "$@"
 
     CHANGES_POSSIBLE=1