Invoices are signed with our own key, but we use a transient payer_key with a
tweak for invoice_requests (and refunds).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Note that other directories were explicitly depending on the generated
file, instead of relying on their (already existing) dependency on
$(LIGHTNINGD_HSM_CLIENT_OBJS), so we remove that.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>