Revert "Make salt in Microdroid's instance img obsolete"

Revert submission 2982081

Reason for revert: There are tests failing which needs modification. Revert for immediate mitigation.
Reverted changes: /q/submissionid:2982081

Change-Id: I3e55e75e5810b06829ce66149516204e5dc81ff1
diff --git a/microdroid_manager/src/verify.rs b/microdroid_manager/src/verify.rs
index 65c32b0..445c1ae 100644
--- a/microdroid_manager/src/verify.rs
+++ b/microdroid_manager/src/verify.rs
@@ -169,14 +169,13 @@
     // verified is consistent with the root hash) or because we have the saved APK data which will
     // be checked as identical to the data we have verified.
 
-    let salt = if cfg!(llpvm_changes) || is_strict_boot() {
-        // Salt is obsolete with llpvm_changes.
-        vec![0u8; 64]
-    } else if let Some(saved_data) = saved_data {
-        // Use the salt from a verified instance.
+    // Use the salt from a verified instance, or generate a salt for a new instance.
+    let salt = if let Some(saved_data) = saved_data {
         saved_data.salt.clone()
+    } else if is_strict_boot() {
+        // No need to add more entropy as a previous stage must have used a new, random salt.
+        vec![0u8; 64]
     } else {
-        // Generate a salt for a new instance.
         let mut salt = vec![0u8; 64];
         salt.as_mut_slice().try_fill(&mut rand::thread_rng())?;
         salt