Use swap operation instead ofClear `parents` after move in
`DisconnectedBlockTransactions::addForBlock` to avoid using the `parents`ensure a known state
variable after movbefore reusing it (which is unsafe due to its undefinethe variable (the standard enforces a valid state),, but
while retaining the performance advantages of move semanticsnot necessarely a known & specific one).
Signed-off-by: Andres Correa Casablanca <andres@thirdhash.com>