block: remove unnecessary drop

Clippy warns that this drop is not doing anything:

  error: calls to `std::mem::drop` with a reference instead of an owned
  value. Dropping a reference does nothing.

The code compiles without the drop, and resizing still works, so just
remove it.

BUG=None
TEST=bin/clippy
TEST=`crosvm disk resize 1 $((10*1024*1024*1024)) $SOCKET`

Change-Id: I1abf26fcd517a76b3007b70eb73545812a0dd79a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2324062
Tested-by: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Commit-Queue: Dylan Reid <dgreid@chromium.org>

devices/src/virtio/block.rs

@@ -441,7 +441,6 @@ impl Worker {
                             }
                         };
 
-                        drop(control_socket);
                         let resp = match req {
                             DiskControlCommand::Resize { new_size } => {
                                 needs_config_interrupt = true;