Create the equivalent of "delinvoice" for payments

[ghost]

As far as I know, there isn't a method for deleting failed or completed payments, like there is for invoices (delinvoice). The aim is to reduce the output of

lightning-cli listpays

[darosior]

I think this can be marked good first issue ?

[ghost]

Now, I delete all payments via:

sqlite3 -header -line lightningd.sqlite3 'DELETE FROM payments'
sqlite3 -header -line lightningd.sqlite3 'DELETE FROM invoices'

in .lightning/bitcoin

[vincenzopalazzo]

@cdecker Maybe this Issue can be close by this PR #3899

[cdecker]

Definitely, thanks for looking this us @vincenzopalazzo

[ghost]

Tested it and it works. Thanks to all involved but in particular @vincenzopalazzo!