[Autofill] Fix naming of kUpdateEntityInstance_{Success,Failure}

We merged AddEntityInstance() and UpdateEntityInstance() into
AddOrUpdateEntityInstance() but didn't remove / update the enum
constants.

Bug: 388590912
Change-Id: Iac66436c2ead56dff577f789159f96881829c1e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6607140
Commit-Queue: Christoph Schwering <schwering@google.com>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Jan Keitel <jkeitel@google.com>
Auto-Submit: Christoph Schwering <schwering@google.com>
Cr-Commit-Position: refs/heads/main@{#1467442}