The table_object instance field is not needed anymore because its
purpose is fulfilled now by the tables field I introduced to support
multiple tables.

In addition I removed {table_instances_} from the {InstanceBuilder}.
This field existed because tables could exist without a WasmTableObject.
With recent changes, WasmTableObjects always exist.

R=mstarzinger@chromium.org

Bug: v8:7581
Change-Id: I5e8e3d2910f7ed7ae74d61eff660f9451b3493ac
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1466641
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60149}