Unfortunately, you need to know precise Partition Keys and Row Keys in order to issue deletes. You do not need to retrieve entities from storage if you know precise RowKeys, but you do need to have them in order to issue batch delete. There is no magic "Delete from table where partitionkey = 10" command like there is in SQL.
However, consider breaking your data up into tables that represent archivable time units. For example in AzureWatch we store all of the metric data into tables that represent one month of data. IE: Metrics201401, Metrics201402, etc. Thus, when it comes time to archive, a full table is purged for a particular month.
The obvious downside of this approach is the need to "union" data from multiple tables if your queries span wide time ranges. However, if your keep your time ranges to minimum quantity, amount of unions will not be as big. Basically, this approach allows you to utilize table name as another partitioning opportunity.