Revert "Upgrade zerocopy to 0.7.5"

Revert submission 2786927-fmayle-zerocopy-update

Reason for revert: broke build

Reverted changes: /q/submissionid:2786927-fmayle-zerocopy-update

Change-Id: I761aec0fd52826d0ee5fdadc5b99b3df474bd827
diff --git a/pvmfw/src/instance.rs b/pvmfw/src/instance.rs
index f2cd6a3..22839cb 100644
--- a/pvmfw/src/instance.rs
+++ b/pvmfw/src/instance.rs
@@ -35,7 +35,6 @@
 use vmbase::virtio::HalImpl;
 use zerocopy::AsBytes;
 use zerocopy::FromBytes;
-use zerocopy::FromZeroes;
 
 pub enum Error {
     /// Unexpected I/O error while accessing the underlying disk.
@@ -175,7 +174,7 @@
     }
 }
 
-#[derive(FromZeroes, FromBytes)]
+#[derive(FromBytes)]
 #[repr(C, packed)]
 struct Header {
     magic: [u8; Header::MAGIC.len()],
@@ -259,7 +258,7 @@
 /// Marks the start of an instance.img entry.
 ///
 /// Note: Virtualization/microdroid_manager/src/instance.rs uses the name "partition".
-#[derive(AsBytes, FromZeroes, FromBytes)]
+#[derive(AsBytes, FromBytes)]
 #[repr(C, packed)]
 struct EntryHeader {
     uuid: u128,
@@ -280,7 +279,7 @@
     }
 }
 
-#[derive(AsBytes, FromZeroes, FromBytes)]
+#[derive(AsBytes, FromBytes)]
 #[repr(C)]
 struct EntryBody {
     code_hash: Hash,