desktop-pwas: Remove unused methods now that link capturing tests are gone

BookmarkAppNavigationBrowserTest is used for intent picker tests and
new window tests, so keep it as a separate test. A lot of its
functionality is copied across a couple of other tests e.g.
HostedAppBrowserTests and we should eventually consolidate all these
utils in a single class.

Bug: 970931
Change-Id: Ifa282155eb61eba5c305d37151fcbd1ee32f7d2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1651531
Commit-Queue: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668274}