Revert "Add os parameter to composd_cmd"

This reverts commit 4dda2fb53ee669c711d19d3f60de9570f56ad245.

Reason for revert: Likely culprit for b/381204036  - verifying through ABTD before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted.

Change-Id: I4cc3ecc7a7f0a51e82574a4c700b2d2bf4ea0d0d
diff --git a/android/composd/src/instance_manager.rs b/android/composd/src/instance_manager.rs
index cb1f7e4..9e94035 100644
--- a/android/composd/src/instance_manager.rs
+++ b/android/composd/src/instance_manager.rs
@@ -46,12 +46,11 @@
         self.start_instance(CURRENT_INSTANCE_DIR, vm_parameters)
     }
 
-    pub fn start_test_instance(&self, prefer_staged: bool, os: &str) -> Result<CompOsInstance> {
+    pub fn start_test_instance(&self, prefer_staged: bool) -> Result<CompOsInstance> {
         let mut vm_parameters = new_vm_parameters()?;
         vm_parameters.name = String::from("ComposdTest");
         vm_parameters.debug_mode = true;
         vm_parameters.prefer_staged = prefer_staged;
-        vm_parameters.os = os.to_owned();
         self.start_instance(TEST_INSTANCE_DIR, vm_parameters)
     }