Describe the Bug:
On a service's page, the on-call user count for each step is one too many

Steps to Reproduce:

1. Go to a service with on-call users
2. Click on a step to expand it
3. See that {x} user(s) assigned is 1 more than the actual user count

Expected Behavior:
User count is the number of users for each step

Actual Behavior:
User count is (number of users + 1) for each step

Screenshots/Stack Traces: