[Profile menu] Update strings to match new picker

This CL adapts terminology in the profile menu to the new terminology
in the profile picker: namely replaces "people" with "profiles".

It also removes two strings not used any more.

Bug: 1063856
Change-Id: I467a6ee9a3e5c4eb2600fd47698ea74e6e3c4fe7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521510


Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824824}