Remove GRPC from element

I came in like a wrecking ball....

I think the grpc server and rpc configuration for the server should be
handled outside of this package.  There are many ways to configure it
and we need more flexability on start and shutdown for grpc services.
Signal handling should be in the caller.

agent.go

@@ -5,7 +5,6 @@ import (
 	"time"
 
 	"github.com/hashicorp/memberlist"
-	"google.golang.org/grpc"
 )
 
 const (
@@ -24,7 +23,6 @@ type Agent struct {
 	members            *memberlist.Memberlist
 	peerUpdateChan     chan bool
 	nodeEventChan      chan *NodeEvent
-	grpcServer         *grpc.Server
 	registeredServices map[string]struct{}
 	memberConfig       *memberlist.Config
 }
@@ -33,7 +31,7 @@ type Agent struct {
 func NewAgent(cfg *Config) (*Agent, error) {
 	updateCh := make(chan bool)
 	nodeEventCh := make(chan *NodeEvent)
-	mc, err := setupMemberlistConfig(cfg, updateCh, nodeEventCh)
+	mc, err := cfg.memberListConfig(updateCh, nodeEventCh)
 	if err != nil {
 		return nil, err
 	}
@@ -42,13 +40,11 @@ func NewAgent(cfg *Config) (*Agent, error) {
 	if err != nil {
 		return nil, err
 	}
-	grpcServer := grpc.NewServer()
 	return &Agent{
 		config:         cfg,
 		members:        ml,
 		peerUpdateChan: updateCh,
 		nodeEventChan:  nodeEventCh,
-		grpcServer:     grpcServer,
 		memberConfig:   mc,
 	}, nil
 }