Suppress dead code clippy lints for crosvm

```
error: field `vm_service` is never read
   -->
packages/modules/Virtualization/android/virtmgr/src/crosvm.rs:372:9
    |
348 | pub struct VmInstance {
    |            ---------- field in this struct
...
372 |     pub vm_service: Mutex<Option<Strong<dyn
IVirtualMachineService>>>,
    |         ^^^^^^^^^^
    |
    = note: `VmInstance` has a derived impl for the trait `Debug`, but
this is intentionally ignored during dead code analysis
    = note: `-D dead-code` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(dead_code)]`
```

Bug: http://b/346588808
Test: ./toolchain/android_rust/tools/test_compiler.py --target aosp_cf_x86_64_phone --image --reuse-prebuilt
Change-Id: I18b77113fe587289d98bd867e841c959b7cacab7
diff --git a/android/virtmgr/src/crosvm.rs b/android/virtmgr/src/crosvm.rs
index 4d19670..f9fbd16 100644
--- a/android/virtmgr/src/crosvm.rs
+++ b/android/virtmgr/src/crosvm.rs
@@ -369,6 +369,7 @@
     /// Callbacks to clients of the VM.
     pub callbacks: VirtualMachineCallbacks,
     /// VirtualMachineService binder object for the VM.
+    #[allow(dead_code)]
     pub vm_service: Mutex<Option<Strong<dyn IVirtualMachineService>>>,
     /// Recorded metrics of VM such as timestamp or cpu / memory usage.
     pub vm_metric: Mutex<VmMetric>,