Reading the serialno property is forbidden

This read always fails so just remove it to avoid selinux denials.

Bug: 63963344
Test: Ran downloader utility on Angelfish over WIFI
Change-Id: I6ce7bb5d161c9d2c4478b5d0fa23dd64b6d599b3
Merged-In: I6ce7bb5d161c9d2c4478b5d0fa23dd64b6d599b3
(cherry picked from commit 1744da2b)