Settings: Convert people_page/ to Polymer class syntax.

Bug: 1206112
Change-Id: I2dd8fc543b28ff3086bf33be8fc039534081d604
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2987627


Commit-Queue: dpapad <dpapad@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#896453}