[FAB-13196] Make Fabric compatible with CouchDB 2.3

CouchDB 2.3 changed format of fields update_seq and purge_seq.
This causes a problem when Fabric maps the CouchDB
JSON resposnes to structs.

Since Fabric doesn't use these fields anyways, they can be removed
from the Fabric CouchDB structs. This will make Fabric
compatible with CouchDB 2.3.

Change-Id: I89f789ef79ea485aa74b99ef047af417a8be044e
Signed-off-by: David Enyeart <enyeart@us.ibm.com>

core/ledger/util/couchdb/couchdb.go

@@ -47,15 +47,13 @@ type DBOperationResponse struct {
 
 // DBInfo is body for database information.
 type DBInfo struct {
-	DbName    string `json:"db_name"`
-	UpdateSeq string `json:"update_seq"`
-	Sizes     struct {
+	DbName string `json:"db_name"`
+	Sizes  struct {
 		File     int `json:"file"`
 		External int `json:"external"`
 		Active   int `json:"active"`
 	} `json:"sizes"`
-	PurgeSeq int `json:"purge_seq"`
-	Other    struct {
+	Other struct {
 		DataSize int `json:"data_size"`
 	} `json:"other"`
 	DocDelCount       int    `json:"doc_del_count"`