We keep the parameter around for future use (e.g. PTLC support?), but clboss
master still sets 'style' to "legacy". Accept, but ignore it.
Reported-by: grubman on #c-lightning (IRC)
Changelog-Deprecated: JSON-RPC: `sendpay` `route` argument `style` "legacy" (don't use it at all, we ignore it now and always use "tlv" anyway).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>