Fix dropaddrindex flag usage message
Fix dropaddrindex flag usage message

Contains the following upstream commits:
- d0f0a2ac02596ff312987fa1fe75972e5bf9a227
  - This commit has already been cherry-picked so it is a NOOP
- 09874f1e9115b56573168cf2d310357356c9d80a

jrick/btcd,jrick/btcd,jcmincke/dcrd,decred/dcrd,jrick/dcrd,jcmincke/dcrd,jrick/btcd,decred/dcrd,jrick/dcrd,jcmincke/dcrd