Deleting property definitions causes intermittent timeout exceptions

Description

Performance of stored proc dbo.netPropertyDefinitionDelete and function dbo.GetExistingScopesForDefinition should be improved when large number of properties exists. Seems to be causing intermittent timeout exceptions, especially in SQL Azure.

This fix indirectly improves speed of stored proc dbo.netPropertyDefinitionCheckUsage (since it also uses function dbo.GetExistingScopesForDefinition),