session: remove estimate_replicas_for_query

Remove estimate_replicas_for_query from Session. A user of this function
can switch to using get_token_endpoints() from ClusterData directly.

It did not make sense for estimate_replicas_for_query() to be in
Session, as this is too much low-level function for Session and doesn't
fit the abstraction of Session.

As a followup, it might make sense to look into whether 
get_token_endpoints() from ClusterData should get removed as well:
ReplicaLocator can be used directly.

This change is a part of our effort to stabilize the API and reduce
the number of pub functions.

Refs #660

Author: avelanarius

examples/compare-tokens.rs

@@ -1,8 +1,9 @@
 use anyhow::Result;
 use scylla::frame::value::ValueList;
+use scylla::routing::Token;
 use scylla::transport::partitioner::{Murmur3Partitioner, Partitioner};
 use scylla::transport::NodeAddr;
-use scylla::{load_balancing, Session, SessionBuilder};
+use scylla::{Session, SessionBuilder};
 use std::env;
 
 #[tokio::main]
@@ -32,16 +33,11 @@ async fn main() -> Result<()> {
         let serialized_pk = (pk,).serialized()?.into_owned();
         let t = Murmur3Partitioner::hash(&prepared.compute_partition_key(&serialized_pk)?).value;
 
-        let statement_info = load_balancing::RoutingInfo {
-            token: Some(scylla::routing::Token { value: t }),
-            keyspace: Some("ks"),
-            is_confirmed_lwt: false,
-            ..Default::default()
-        };
         println!(
-            "Estimated replicas for query: {:?}",
+            "Token endpoints for query: {:?}",
             session
-                .estimate_replicas_for_query(&statement_info)
+                .get_cluster_data()
+                .get_token_endpoints("ks", Token { value: t })
                 .iter()
                 .map(|n| n.address)
                 .collect::<Vec<NodeAddr>>()

scylla/src/transport/session.rs

@@ -1451,20 +1451,6 @@ impl Session {
         Ok(Some(tracing_info))
     }
 
-    // Returns which replicas are likely to take part in handling the query.
-    // If a list of replicas cannot be easily narrowed down, all available replicas
-    // will be returned.
-    pub fn estimate_replicas_for_query(&self, statement: &RoutingInfo) -> Vec<Arc<Node>> {
-        let cluster_data = self.cluster.get_data();
-        match statement.token {
-            Some(token) => {
-                let cluster_data = self.cluster.get_data();
-                cluster_data.get_token_endpoints(statement.keyspace.unwrap_or(""), token)
-            }
-            None => cluster_data.get_nodes_info().to_owned(),
-        }
-    }
-
     // This method allows to easily run a query using load balancing, retry policy etc.
     // Requires some information about the query and two closures
     // First closure is used to choose a connection