Remove Rackspace handling from property images service

[plittlewood-rpt]

Background context Now that all customers have migrated from Rackspace to AWS infrastructure, we can remove areas of our codebase that run business logic around the filesystem depending on where the customer's data and assets is hosted.

Specification

• Project: Reapit.Services.PropertyImages
• Update FileStorageClient to remove any behaviour where we check to see if the customer uses Rackspace (there is a helper method in the CustomerPlatformIdentity object for this purpose

[HollyJoyPhillips]

Internal reference: PBI-5718