Remove placeholder secret used with keymint

Migration to diced removed the need for keymint and this means of
passing the value between services.

Bug: 215747811
Test: atest MicrodroidTests
Change-Id: If8e35243e3ded2709a03ff7150a205be3963e7a1
diff --git a/microdroid_manager/src/main.rs b/microdroid_manager/src/main.rs
index 4420a49..960759e 100644
--- a/microdroid_manager/src/main.rs
+++ b/microdroid_manager/src/main.rs
@@ -26,7 +26,7 @@
 use glob::glob;
 use idsig::V4Signature;
 use itertools::sorted;
-use log::{error, info, warn};
+use log::{error, info};
 use microdroid_metadata::{write_metadata, Metadata};
 use microdroid_payload_config::{Task, TaskType, VmPayloadConfig};
 use once_cell::sync::OnceCell;
@@ -182,11 +182,6 @@
     }
     mount_extra_apks(&config)?;
 
-    let fake_secret = "This is a placeholder for a value that is derived from the images that are loaded in the VM.";
-    if let Err(err) = rustutils::system_properties::write("ro.vmsecret.keymint", fake_secret) {
-        warn!("failed to set ro.vmsecret.keymint: {}", err);
-    }
-
     // Wait until apex config is done. (e.g. linker configuration for apexes)
     // TODO(jooyung): wait until sys.boot_completed?
     wait_for_apex_config_done()?;