This reverts commit f30d261e69.
The custom HD path option was found to be unsafe to use, because the
displayed list of accounts would differ depending on which application
was open on the Ledger device. Essentially Ledger was accepting invalid
inputs, and returning junk responses.
This was too dangerous to ship, as it could leave users with an account
that they can't reliably recover. If we don't know how the derivation
is happening, then allowing this import puts our users at risk of
losing funds.
We can re-introduce this functionality after adding validation to
ensure that we only allow inputs that are handled correctly by Ledger.
beb6047384