core: Move triggers into separate binary: ostree-run-triggers

I'm trying to keep ostree as being closer to just being the versioning
filesystem, so let's split out the triggers into a different binary
(although still namespaced ostree-).

src/libostree/ostree.h

@@ -24,7 +24,6 @@
 
 #include <ostree-core.h>
 #include <ostree-repo.h>
-#include <ostree-checkout.h>
 #include <ostree-mutable-tree.h>
 #include <ostree-repo-file.h>