Remove unused parameter in PrintBackend::CreateInstanceImpl()

After Cloud Print code got removed, the `print_backend_settings`
parameter in PrintBackend::CreateInstanceImpl() is always null. Remove
it and associated dead code.

Change-Id: I46a2784f0fb6d100cafc6be2a88c9b942e5fdfec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4564793


Reviewed-by: Alan Screen <awscreen@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1149430}