fixup! Add support for worker state callbacks

Author: JamesWrigley

src/cluster.jl

@@ -955,7 +955,11 @@ you do this).
 """
 add_worker_starting_callback(f::Base.Callable; key=nothing) = _add_callback(f, key, worker_starting_callbacks;
                                                                             arg_types=Tuple{ClusterManager, Dict})
+"""
+    remove_worker_starting_callback(key)
 
+Remove the callback for `key` that was added with [`add_worker_starting_callback()`](@ref).
+"""
 remove_worker_starting_callback(key) = _remove_callback(key, worker_starting_callbacks)
 
 """