Remove unused ThreadSafeHandleURI from ui_interface
Remove unused ThreadSafeAskFee from ui_interface

ThreadSafeAskFee is effectively unused. It is only called
when the fAskFee parameter on SendMoney or SendMoneyToDestination
is true, which never happens. Remove it.
qt: status WalletModel::Aborted is no longer used

Aborting transactions happens in the GUI now as it should,
not the backend.
Merge pull request #3415

4a61c39 qt: status WalletModel::Aborted is no longer used (Wladimir J. van der Laan)
ca2c83d Remove unused ThreadSafeAskFee from ui_interface (Wladimir J. van der Laan)
37e67d3 Remove unused ThreadSafeHandleURI from ui_interface (Wladimir J. van der Laan)