Use OnceCallback for Mojo binding connection error handlers.

Use RepeatingCallback for BindingSet connection error handlers because
the error handlers can be called for each entry in the set.

BUG=NONE
TEST=mojo_public_bindings_unittests

Review-Url: https://codereview.chromium.org/2932193002
Cr-Commit-Position: refs/heads/master@{#478798}


CrOS-Libchrome-Original-Commit: 14ae013de771be3f72bc59c407e0d677bbc093d8