Move pagination tests to appropiate location

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.