migrate delete collection to grpc API on volume server

weed/server/volume_grpc_admin.go

@@ -0,0 +1,22 @@
+package weed_server
+
+import (
+	"context"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/pb/volume_server_pb"
+)
+
+func (vs *VolumeServer) DeleteCollection(ctx context.Context, req *volume_server_pb.DeleteCollectionRequest) (*volume_server_pb.DeleteCollectionResponse, error) {
+
+	resp := &volume_server_pb.DeleteCollectionResponse{}
+
+	err := vs.store.DeleteCollection(req.Collection)
+
+	if err != nil {
+		glog.V(3).Infof("delete collection %s: %v", req.Collection, err)
+	}
+
+	return resp, err
+
+}