1. anchor_to_remote_redeem => bitcoin_wscript_to_remote_anchored,
which matches other witness script producing functions and makes
it clear that it's a to_remote variant.
2. is_anchor_witness_script => is_to_remote_anchored_witness_script
makes it clear that it's about a to_remote output (as altered
when anchors are enabled) not an anchor output!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>