Remove leftover send_tab_to_self function declarations

The implementations of these functions were removed, but not their
declarations.

Bug: None
Change-Id: I73d726dfce004de3df74790d17b4bf594ec96e6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521736


Commit-Queue: Victor Vianna <victorvianna@google.com>
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824890}