[Enhancement] Remove service account code in main

[derek-ho]

Is your feature request related to a problem?
If there is no plan to backport service accounts feature to 2.x, then the code should be removed. Because of this difference, code that touches user pages may conflict on the backport, leading to manual backports and misses during reviews (including recent autocut for 2.15 release).
What solution would you like?
Removal of service accounts code to consolidate main and 2.x, if there is no plan to release
What alternatives have you considered?
None
Do you have any additional context?
None

[derek-ho]

Related issue: #1999

[scrawfor99]

[Triage] Hi @derek-ho, for filing this issue. This seems like a good request since we are not currently looking at moving Service Accounts back to 2.x. Will mark as triaged.