Revert "[FIX] core: close cursors open during tests"

Not necessary anymore thanks to commit
731b9f60.

The test cursors were leaked by the _check_accounting_configured()
function used to manually skip some tests.

After 731b9f60 the tests are skipped cleanly without
leaking cursors, so this became redundant with the reset()
function already present in the TransactionCase cleanups.

This reverts commit 57b14988.