Drop `create_inbound_payment*_legacy` breaking downgrade to 0.0.103

[rust-lightning] / pending_changelog / no-legacy-payments.txt

 * Legacy inbound payment creation has been removed, thus there is no way to
   create a pending inbound payment which will still be claimable on LDK
   0.0.103 or earlier. Support for claiming such payments is still retained,
   however is likely to be removed in the next release.