[devcoordinator] REVERT: Fix buggy composite device behavior

This reverts commit 75b35cea.

Reason for revert: This CL is a suspect for the currently red fuchsia-roller;  it fails the /boot/test/ddk/platform-bus-test test.

Original change's description:
> [devcoordinator] Fix buggy composite device behavior
>
> If a component was a device with MUST_ISOLATE set on it, we would try to
> bind to the non-proxied side of it, which doesn't speak the device
> protocols.
>
> Change-Id: I64eaccec5d51997f4374d0277b040a952f681667

TBR=teisenbe@google.com,abarth@google.com,jocelyndang@google.com

Change-Id: Id9d48682336ea648599cfead60444c5074c4ae1e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true