Fix PWA metrics (part 1 / N).

This CL removes a confusing and unnecessary piece of functionality from
PWAs. With this CL, we always show PWA link/tooltip for PWA
site-settings.

Previously, WebContents tracked whether they were launched as a PWA, and
whether they were ever parented into an app-window. If either is ever
true, then site settings would show a PWA link/tooltip. This is
confusing because a stateless piece of UI (site settings) reflects the
historical state of the WebContents. This means that a user can have two
tabbed PWAs next to each other (one of which had been in an app window,
the other of which had not) and site settings would show different ui
even though they are functionally identical now.

Change-Id: I461da7120591ff3cbd360da811a708c596c83cf4
Bug: 358404364
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5912367
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1365845}