3a3a9f9 Ignore old format estimation file (Murch)
Pull request description:
The fee estimation data format changed from 0.14.x to 0.15.0, so we should no longer read the old data. H/T @jnewbery, @morcos
Pending testing.
Tree-SHA512: c8e3824dbdd8f6730133d5ad20b00995e9a63ab54431158a91e2f4d2aba5763b8aa698bce1fffca2713ba3a162e23d8fcd6e3efb9847b015c2e1e8725398150b