Remove partName, partETag requirement (#9044)

This is a precursor change before versioning,
removes/deprecates the requirement of remembering
partName and partETag which are not useful after
a multipart transaction has finished.

This PR reduces the overall size of the backend
JSON for large file uploads.

cmd/encryption-v1_test.go

@@ -280,15 +280,11 @@ func TestGetDecryptedRange_Issue50(t *testing.T) {
 		Parts: []ObjectPartInfo{
 			{
 				Number:     1,
-				Name:       "part.1",
-				ETag:       "etag1",
 				Size:       297580380,
 				ActualSize: 297435132,
 			},
 			{
 				Number:     2,
-				Name:       "part.2",
-				ETag:       "etag2",
 				Size:       297580380,
 				ActualSize: 297435132,
 			},