proto: remove deprecated SendPayment, SendToRoute, TrackPayment RPCs

Remove the following deprecated RPC definitions that were announced for
removal in 0.21 via the 0.20 release notes:

lnrpc:
  - SendPayment (bidirectional streaming)
  - SendPaymentSync
  - SendToRoute (bidirectional streaming)
  - SendToRouteSync

routerrpc:
  - SendPayment (streaming)
  - SendToRoute
  - TrackPayment (streaming)

Also remove the now-unused PaymentState enum and PaymentStatus message
that were only used by the deprecated TrackPayment response stream, plus
the corresponding REST annotations from the yaml files. Regenerate all
protobuf, gRPC, REST gateway, JSON, and swagger files.

Author: erickcestari

docs/rest/websockets.md

@@ -130,8 +130,8 @@ ws.on('open', function() {
     // This empty message will be ignored by the channel acceptor though, this
     // is just for telling the grpc-gateway library that it can forward the
     // request to the gRPC interface now. If this were an RPC where the client
-    // always sends the first message (for example the streaming payment RPC
-    // /v1/channels/transaction-stream), we'd simply send the first "real"
+    // always sends the first message (for example the HTLC interceptor RPC
+    // /v2/router/htlcinterceptor), we'd simply send the first "real"
     // message here when needed.
     ws.send('{}');
 });

lnrpc/README.md

@@ -69,15 +69,6 @@ description):
      * Attempts to close a target channel. A channel can either be closed
        cooperatively if the channel peer is online, or using a "force" close to
        broadcast the latest channel state.
-  * SendPayment
-     * Send a payment over Lightning to a target peer.
-  * SendPaymentSync
-     * SendPaymentSync is the synchronous non-streaming version of SendPayment.
-  * SendToRoute
-    * Send a payment over Lightning to a target peer through a route explicitly
-      defined by the user.
-  * SendToRouteSync
-    * SendToRouteSync is the synchronous non-streaming version of SendToRoute.
   * AddInvoice
      * Adds an invoice to the daemon. Invoices are automatically settled once
        seen as an incoming HTLC.