init: remove restorecon() from util.cpp

restorecon() has become nothing more than a small wrapper around
selinux_android_restore().  This itself isn't super problematic, but
it is an obstacle for compiling util.cpp on the host as that function
is not available on the host.

Bug: 36970783
Test: Boot bullhead
Change-Id: I7e209ece6898f9a0d5eb9e5d5d8155c2f1ba9faf