Move pagination tests to appropiate location

[kevin-pease]

Currently, pagination functionality for requests are being tested in assets/all_assets_request.rs. Since all code concerning pagination in requests (i.e. set cursors, order, limit) has been moved to a macro, it would make more sense to test it there.

Identical (and therefore duplicate) tests also occur in some other endpoints (for example all_claimable_balances_request). These can be removed as well.