Revert "Add .arcconfig to project root"

This reverts commit 0ce21aea083b4367ed0ec88c2a1fc92aa27177d9.

.arcconfig

@@ -1,5 +0,0 @@
-{
-	"phabricator.uri": "https://source.syncthing.net/",
-	"project_id": "syncthing",
-	"project.name": "syncthing"
-}