kvserver: remove unused snapshot log entry code

We used to have to send the raft log along with snapshots as a result of
(in the olden days) requiring all replicas to agree on the truncated
state. This hasn't been (generally) true as of v19.1 (cockroachdb#35701), though it
was still a possibility until v22.1 (cockroachdb#58088). This commit removes the
corresponding code.

Release note: None

pkg/kv/kvserver/raft.proto

@@ -195,12 +195,9 @@ message SnapshotRequest {
   // A RocksDB BatchRepr. Multiple kv_batches may be sent across multiple request messages.
   bytes kv_batch = 2 [(gogoproto.customname) = "KVBatch"];
 
-  // These are really raftpb.Entry, but we model them as raw bytes to avoid
-  // roundtripping through memory. They are separate from the kv_batch to
-  // allow flexibility in log implementations.
-  repeated bytes log_entries = 3;
-
   bool final = 4;
+
+  reserved 3;
 }
 
 message SnapshotResponse {