Remove FrameDetached and FrameWillClose listeners from AutofillAgent.

      AutofillAgent::FrameDetached is no longer necessary because form_cache_ only holds the forms for a single frame.
AutofillAgent::FrameWillClose is only called on the actual closing frame (which might be a parent frame).
AutofillAgent::FrameDetached can't take the place of AutofillAgent::FrameWillClose because the RenderFrame disables sending IPCs during detachment.

Therefore, move the automatic closing of rAc from the renderer (autofill_agent.cc) to the browser (chrome_autofill_client.cc).

For PasswordAutofillAgent, add FrameDetached to RenderFrameHost.

BUG=433486

Review URL: https://codereview.chromium.org/796493004

Cr-Commit-Position: refs/heads/master@{#310162}