api/faq: add entry on incremental xDS. (#10876)

Also remove some stale comments around delta xDS in ConfigSource.

Fixes #10836

Signed-off-by: Harvey Tuch <htuch@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 4ee310ec07a4e0e775626fe8c652726b4151b8e9

envoy/api/v2/core/config_source.proto

@@ -57,10 +57,6 @@ message ApiConfigSource {
     // Using the delta xDS gRPC service, i.e. DeltaDiscovery{Request,Response}
     // rather than Discovery{Request,Response}. Rather than sending Envoy the entire state
     // with every update, the xDS server only sends what has changed since the last update.
-    //
-    // DELTA_GRPC is not yet entirely implemented! Initially, only CDS is available.
-    // Do not use for other xDSes.
-    // [#comment:TODO(fredlas) update/remove this warning when appropriate.]
     DELTA_GRPC = 3;
   }
 

envoy/config/core/v3/config_source.proto

@@ -58,10 +58,6 @@ message ApiConfigSource {
     // Using the delta xDS gRPC service, i.e. DeltaDiscovery{Request,Response}
     // rather than Discovery{Request,Response}. Rather than sending Envoy the entire state
     // with every update, the xDS server only sends what has changed since the last update.
-    //
-    // DELTA_GRPC is not yet entirely implemented! Initially, only CDS is available.
-    // Do not use for other xDSes.
-    // [#comment:TODO(fredlas) update/remove this warning when appropriate.]
     DELTA_GRPC = 3;
   }
 

envoy/config/core/v4alpha/config_source.proto

@@ -59,10 +59,6 @@ message ApiConfigSource {
     // Using the delta xDS gRPC service, i.e. DeltaDiscovery{Request,Response}
     // rather than Discovery{Request,Response}. Rather than sending Envoy the entire state
     // with every update, the xDS server only sends what has changed since the last update.
-    //
-    // DELTA_GRPC is not yet entirely implemented! Initially, only CDS is available.
-    // Do not use for other xDSes.
-    // [#comment:TODO(fredlas) update/remove this warning when appropriate.]
     DELTA_GRPC = 3;
   }