Fix bogus reentrancy from read_event -> do_attempt_write_data

`Julian Knutsen <julianknutsen@users.noreply.github.com>` pointed
out in a previous discussion that `read_event` can reenter user
code despite the documentation stating explicitly that it will not.

This was addressed in lightningdevkit#456 by simply codifying the reentrancy, but
its somewhat simpler to just drop the `do_attempt_write_data` call.

Ideally we could land most of Julian's work, but its still in need
of substantial git history cleanup to get it in a reviewable state
and this solves the immediate issue.

Author: TheBlueMatt

lightning/src/ln/peer_handler.rs

@@ -794,7 +794,7 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, L: Deref> PeerManager<D
 											}
 										};
 
-										if let Err(handling_error) = self.handle_message(&mut peers.peers_needing_send, peer, peer_descriptor.clone(), message){
+										if let Err(handling_error) = self.handle_message(&mut peers.peers_needing_send, peer, peer_descriptor.clone(), message) {
 											match handling_error {
 												MessageHandlingError::PeerHandleError(e) => { return Err(e) },
 												MessageHandlingError::LightningError(e) => {
@@ -808,8 +808,6 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, L: Deref> PeerManager<D
 						}
 					}
 
-					self.do_attempt_write_data(peer_descriptor, peer);
-
 					peer.pending_outbound_buffer.len() > 10 // pause_read
 				}
 			};