Shimless: Convert fake_shimless_rma_service_test.js to ts

- Fix all ts errors and use ts styling.
- Convert tests to async.
- Remove unneeded tests that did not add value.
- Remove the special case for `chooseManuallyDisableWriteProtect()` that
  made it skip ahead two states. It's easier if each page in the fake
  service behaves the exact same (clicking next always moves to the next
  state in the list).

Test: browser_tests --gtest_filter=ShimlessRmaApp.FakeShimlessRmaService
Bug: b:315002705
Change-Id: I11882bb9903ec67136cfefd4f95e15645444499b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5399130


Reviewed-by: Ashley Prasad <ashleydp@google.com>
Commit-Queue: Gavin Williams <gavinwill@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280000}