Removing Dataloader as a parameter in PrivacyEngine

[JohnlNguyen]

Feature

Currently, PrivacyEngine requires a dataloader to be passed in as a parameter to calculate the sample rate (see code). This is the only time the we use the dataloader (see grep). Here is no other need for the dataloader asides from that.

Alternatives

I suggest we let the user pass in the sample rate as an optional parameter instead and remove the dependency on the dataloader.

Additional context

We only depend on the sample rate to calculate the privacy budget not the dataloader, Am I missing something here?