Remove disk serial number from /tmp/machine-info

This is no longer needed as server-backed state key generation for
froced re-enrollment is now handled via different code path.

BUG=chromium:358213
TEST=Compiles and passes tests.

Change-Id: Ie6956fa416e91222a98b54485a27e8939c85396b
Reviewed-on: https://chromium-review.googlesource.com/199720
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Commit-Queue: Mattias Nissler <mnissler@chromium.org>
Tested-by: Mattias Nissler <mnissler@chromium.org>
diff --git a/init/machine-info.conf b/init/machine-info.conf
index 825af00..215f69c 100644
--- a/init/machine-info.conf
+++ b/init/machine-info.conf
@@ -43,22 +43,6 @@
       # Dump full information in the VPD, including the serial number.
       dump_vpd_log --full --stdout
     fi >> $MACHINE_INFO
-
-    # Dump the disk serial number. It is used to generate non-predictable
-    # opaque machine identifiers by running it through a cryptographic hash
-    # function along with other stable machine information and a time stamp.
-    # The disk serial number is chosen here because it provides some entropy
-    # only known to the device. Device serial numbers, MAC addresses etc. are
-    # public identifiers potentially known to the environment and/or servers.
-    # Solely relying on public identifiers for opaque identifier derivation
-    # would increase the chances of external parties being able to forge valid
-    # opaque identifiers and defeat non-predictability.
-    ROOTDEV=$(rootdev -s -d)
-    udevadm trigger --sysname-match="${ROOTDEV##/dev/}"
-    udevadm settle
-    udevadm info --query=property --name="$ROOTDEV" |\
-        awk -F = '/^ID_SERIAL=/ { print "root_disk_serial_number=" $2 }' \
-        >> $MACHINE_INFO
   fi
 end script