fix(customs): Don't call customs on the GET /recoveryCodes/exist endpoint

[vbudhram]

Because

• This endpoint is authenticated with a sessionToken, we don't need to check customs
• This might cause a user to get rate limited unexpectedly

This pull request

• Remove the customs check

Issue that this pull request solves

Closes: https://mozilla-hub.atlassian.net/browse/FXA-10880

Checklist

• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).