ExtensionManagementApiTest cleanup

DesktopPWAsWithoutExtensions has shipped.

The test case GenerateAppForLink no longer needs to
be parameterized.

Bug: 1065748
Change-Id: I1893b45f7183ccb24c51149c7189aed62751fa5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2459256


Auto-Submit: Eric Willigers <ericwilligers@chromium.org>
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815284}