Minor documentation change for clarifying aggregate vs nesting for work schedules

Original issue: https://forums.buildingsmart.org/t/minor-documentation-change-for-clarifying-aggregate-vs-nesting-for-work-schedules/3563

Given the following quote for IfcWorkSchedules:

> Nesting
>
> The [Object Nesting](http://localhost:8001/schema/templates/object-nesting.htm) concept applies to this entity.
>
> A work schedule can include other work schedules as sub-items through [IfcRelNests](http://localhost:8001/schema/ifckernel/lexical/ifcrelnests.htm) relationship.
>
> Aggregation
>
> The [Aggregation](http://localhost:8001/schema/templates/aggregation.htm) concept applies to this entity.
>
> **A work schedule can include other work schedules as sub-items.** If not included in another work schedule it might be a part of a work plan ([IfcWorkPlan](http://localhost:8001/schema/ifcprocessextension/lexical/ifcworkplan.htm)) defined through [IfcRelAggregates](http://localhost:8001/schema/ifckernel/lexical/ifcrelaggregates.htm) relationship.

The bolded sentence (emphasis mine) may be misinterpreted that aggregation is the concept used to put a workschedule as a sub-item of another work schedule. I believe this is not the intention. The intention is that Work Schedule -> Work Schedule is **nesting**, and Work Plan -> Work Schedule is **aggregation**.

I propose to remove the sentence in bold to remove this potential confusion.

Start with the IfcWorkSchedules documentation quoted in the issue and compare its Nesting and Aggregation sections with the linked IFC concepts. Remove the sentence stating that a work schedule can include other work schedules as sub-items, while retaining the distinction between nested work schedules and aggregated work plans.

Written by the indexing model from the issue text.