agent: Remove unused max monthly spend reached error (#30615)

This PR removes the code for showing the max monthly spend limit reached
error, as it is no longer used.

Release Notes:

- N/A
7cad943fdeMarshall Bowers committed on 5/13/2025, 9:43:13 AM· committed by GitHubparent29da105
6 files changedLine totals unavailable