This removes dangerous accessors method from the arguments object
accessor classes. The shape of an arguments object might transition,
turning the fields into dictionary mode, making the accessors invalid.

It also fixes a bug in the reported number of embedder fields on the
arguments object.

R=ishell@chromium.org
TEST=cctest/test-api/InternalFieldsOfRegularObjects

Change-Id: Ib7a73608c6236fe8864434e0cfdcb754ae012a75
Reviewed-on: https://chromium-review.googlesource.com/636368
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47643}