[lens] Clean up `lens::{AppendOrReplace...Request,IsValidLensResultUrl}`

These have no callers and no coverage [0] in any test suite.

[0]: https://analysis.chromium.org/coverage/p/chromium/file?host=chromium.googlesource.com&project=chromium/src&ref=refs/heads/main&revision=c37f119c698fbb959eb84939a52ed54df114240e&path=//components/lens/lens_url_utils.cc&platform=linux&test_suite_type=any&modifier_id=0

Bug: None
Change-Id: Ib6f3bc9d3029575b9f062595afdeb616de6de252
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6990178
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Auto-Submit: Jonathan Lee <jonathanjlee@google.com>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1521810}