composite disk: no support for multi-file partition

We don't need to support multi-file partition for composite disk images.
This will make the code simpler.

BUG=b:190503456
TEST=cargo test

Change-Id: I9e115ec73ad451ea46fe91c0d0a3c2e85aa1f010
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3058835
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-by: Andrew Walbran <qwandor@google.com>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Jooyung Han <jooyung@google.com>
Auto-Submit: Jooyung Han <jooyung@google.com>
diff --git a/src/main.rs b/src/main.rs
index 0da7b8d..fd06ccf 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -37,9 +37,7 @@
 use devices::{Ac97Backend, Ac97Parameters};
 use disk::QcowFile;
 #[cfg(feature = "composite-disk")]
-use disk::{
-    create_composite_disk, create_disk_file, ImagePartitionType, PartitionFileInfo, PartitionInfo,
-};
+use disk::{create_composite_disk, create_disk_file, ImagePartitionType, PartitionInfo};
 use vm_control::{
     client::{
         do_modify_battery, do_usb_attach, do_usb_detach, do_usb_list, handle_request, vms_request,
@@ -2358,12 +2356,10 @@
                     .map_err(|e| error!("Failed to get length of partition image: {}", e))?;
                 Ok(PartitionInfo {
                     label: label.to_owned(),
-                    files: vec![PartitionFileInfo {
-                        path: Path::new(path).to_owned(),
-                        size,
-                    }],
+                    path: Path::new(path).to_owned(),
                     partition_type: ImagePartitionType::LinuxFilesystem,
                     writable: false,
+                    size,
                 })
             } else {
                 error!(