fix: remove unused assignment (GoogleCloudPlatform#8979)

Per issue GoogleCloudPlatform#8977 this assignment is not needed as it is overwritten three statements later.

Co-authored-by: Leah E. Cole <[email protected]>
Co-authored-by: gcf-merge-on-green[bot] <60162190+gcf-merge-on-green[bot]@users.noreply.github.com>
Co-authored-by: Karl Weinmeister <[email protected]>

Author: 4 people

monitoring/snippets/v3/cloud-client/snippets.py

@@ -89,7 +89,6 @@ def list_time_series(project_id):
 
     client = monitoring_v3.MetricServiceClient()
     project_name = f"projects/{project_id}"
-    interval = monitoring_v3.TimeInterval()
 
     now = time.time()
     seconds = int(now)