How to stop the log shipping alert which sending the error message 14421?

How to stop the log shipping alert which sending the below error message?

Error Message:

Over the previous interval, there were 5 occurrences of the following event.

Logfile: Application
Event Type: Error
Event ID: 14421
Computer: XXXXXXXX
Source: MSSQL$SQL2008
Text:
The log shipping secondary database Servername \SQL2008.Databasename has restore threshold of 45 minutes and is out of sync.
No restore was performed for 9426 minutes. Restored latency is 8 minutes. Check agent log and logshipping monitor information.

Cause:

Database which involved in source as well in destination server for log shipping setup is not available. Because database dropped by somebody.

Resolution:

The database name entry is found in the below logshipping tables that are referencing the alert jobs LSAlert_ XXXXXXXX \SQL2008 and LSAlert_YYYYYYY\SQL2008 in both primary and secondary server.

Action Taken:

 By removing the record entry in the below log shipping tables corresponding to the log shipping database, Alerts stating above error message 14421 won’t come anymore.

Select * from msdb.dbo.log_shipping_monitor_primary
select * from msdb.dbo.log_shipping_monitor_secondary

Delete from msdb.dbo.log_shipping_monitor_primary where primary_database='logshippingdatabasename'

Delete from msdb.dbo.log_shipping_monitor_secondary where secondary_database='logshippingdatabasename'