How to reduce the number of things SQL Server puts in the windows event viewer?
Note: This will not limit what gets logged. It justs stops logging in Windows Event log.

There are some stuff that you can prevent like - successful completion of log backups using Trace Flag 3226 

Have a look at -n startup parameter.

From Database Engine Service Startup Options :


  Does not use the Windows application log to record SQL Server events. If you start an instance of SQL Server with -n, we recommend that you also use the -e startup option. Otherwise, SQL Server events are not logged.