[Alerting] Alert list was not refreshed after deleting alerts

[hendry-lim]

Kibana version: 7.8.0

Elasticsearch version: 7.8.0

Server OS version: Alpine

Browser version: Firefox 78.0.2

Browser OS version: openSUSE

Original install method (e.g. download page, yum, from source, etc.): Docker

Describe the bug:
Alert list was not refreshed after deleting alerts.

Steps to reproduce:
More than 10 alerts will be needed to replicate/simulate the issue.

1. In Kibana, go to Management --> Alerts and Actions
2. Select multiple or all alerts within a page
3. Delete selected alerts
4. The alert list became blank (if all alerts within the page were deleted), or the number of alerts in the page reduced by the number of deleted alerts.

Expected behavior:
Alert list should be refreshed.
Alert list should display the same number of alerts based on the selected Rows per page value.

Screenshots (if relevant):

Expand

[hendry-lim]

Issue persists in 7.9.0-SNAPSHOT.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)