[TLDD] Moving tab tearing FF check to caller.

Having the check in MultiInstanceManager was causing tab drag to fail since tab tearing FF is disabled.

Bug: 345788473
Change-Id: I897362d67abf1ad4988a4a1d2f9d1461933dde84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5616850


Reviewed-by: Aishwarya Rajesh <aishwaryarj@google.com>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Commit-Queue: Sirisha Kavuluru <skavuluru@google.com>
Cr-Commit-Position: refs/heads/main@{#1313053}