Send only reads with (:target env) true, returned by mutate's :remote

[petterik]

Use case:

{:mutate 
  (fn [env k p] 
    (when (and (= 'foo/conj k) (:target env))
      [true :query/foo]))
 :read
  (fn [env k p]
    (when (and (= :query/foo k) (:target env))
      false))}

((parser *1) {} '[(foo/conj)] :remote)
;; should equal '[(foo/conj)]
;; not '[(foo/conj) :remote]
;; because :query/foo is not a remote read
;; even though the mutate suggested that it is.