The restorecon_recursive directive in init is only applied if the
file_contexts file changed between builds, but not necessarily if any
file or folder inside /mnt/vendor/persist/ has changed.
The restorecon code checks whether an xattr named
"security.sehash" contains a string that matches the current
combined hashes of the SELinux context files and skips restoring labels
if there is a match, see
https://android.googlesource.com/platform/external/selinux/+/refs/tags/android-9.0.0_r35/libselinux/src/android/android_platform.c#1546
Force wiping that xattr so that restorecon always runs since it's not
very expensive (there are currently only about 50 files on /persist).
The restorecon is needed to fix issues such as wrong stock labels on
/mnt/vendor/persist/sensors/:
sensors_persist_file -> persist_sensors_file
Change-Id: Ic0cd848836ee550499d9236f56ed6e939e35f01e
a13246a7fc