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This CL polishes the Phone Hub panel including:
  - Relayouts the continue browsing chip.
  - Removes the separators.

Screenshot: https://screenshot.googleplex.com/8uHj96SrADLFmAc.png

Misc: removes unused headers.

BUG=1106937,1126208

Change-Id: I0c1c2bef1883c6a8a188fde7c287a0a1bddbdf5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2494023
Commit-Queue: Meilin Wang <meilinw@chromium.org>
Reviewed-by: Tim Song <tengs@chromium.org>
Reviewed-by: Andre Le <leandre@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820965}