Clean up unused method to fetch all PlusAddress from the server.

Plus addresses are not requested directly from the server anymore,
instead these arrive via sync. Therefore we're removing unnecessary API
call methods like `GetAllPlusAddresses` from the http client.

Bug: 322147254
Change-Id: I70177713d997b4aca46c2d1098b576d13323af6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5802947
Commit-Queue: Norge Vizcay <vizcay@google.com>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Reviewed-by: Rainhard Findling <rainhard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1345900}