[iOS] Fix Password Bottom Sheet related EG tests

This CL fixes 2 tests:
1) testUpdatePromptAppearsOnFormSubmission: This should only run
   with kIOSPasswordBottomSheet enabled. Made sure this was done
   in the test's setup.
2) testOpenPasswordBottomSheetDeletePassword: The test was missing
   a reauth mock for the password deletion action.

Bug: 1448911, 1422341
Change-Id: I6dd367e963bd929381ae2729f07459b8fed37dc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4582811


Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1152624}