[Butter STTS] Adapt strings of "no target device" state on Android

Mock (sorry, Googlers only)
https://docs.google.com/presentation/d/1w4me9wINwMW2UD-uuSQGMKiWuqkX9GDfAFvSM74Pt00/edit#slide=id.ge5622f64da_0_48
Implementation
crbug.com/1245915#c1

The current strings refer to "enabling sync" as the requirement to
share a tab. This requirement becomes "sign-in" with Butter STTS, so
the strings are updated to reflect that.

Bug: 1245915
Change-Id: Id9426cac0f8c3ccf2c1e854011286b3e30e26db1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3139913


Auto-Submit: Victor Vianna <victorvianna@google.com>
Reviewed-by: Kyle Milka <kmilka@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#919281}