Rename Size_ to Size

Previouslty "Size" was reserved by protoc-gen-gogoctrd and user-generated
"Size" was automatically renamed to "Size_" to avoid conflicts.

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

task_opts.go

@@ -69,7 +69,7 @@ func WithTaskCheckpoint(im Image) NewTaskOpts {
 			if m.MediaType == images.MediaTypeContainerd1Checkpoint {
 				info.Checkpoint = &types.Descriptor{
 					MediaType:   m.MediaType,
-					Size_:       m.Size,
+					Size:        m.Size,
 					Digest:      m.Digest.String(),
 					Annotations: m.Annotations,
 				}