Retire InstallManagerBookmarkAppTest

DesktopPWAsWithoutExtensions has shipped. The test is no longer
needed.

Retiring the test also closes flaky test bugs.

Bug: 1065748,1043466,1043806,1044900
Change-Id: I1344f2a2373ead35cf0700a26cdbf1af713e7bc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2455567Reviewed-by: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815080}

chrome/browser/web_applications/extensions/BUILD.gn

@@ -56,7 +56,6 @@ source_set("unit_tests") {
     "bookmark_app_install_finalizer_unittest.cc",
     "bookmark_app_util_unittest.cc",
     "externally_installed_web_app_prefs_unittest.cc",
-    "install_manager_bookmark_app_unittest.cc",
     "pending_app_install_task_unittest.cc",
     "web_app_policy_manager_unittest.cc",
     "web_app_provider_unittest.cc",