genfs_contexts

When moving SELinux rules from file_contexts to genfs_contexts, we
added some genfs rules to label specific files.  It turns out that one
of those files was the prefix of some other files, and since genfs
does prefix-labeling, those other files had their labels changed.

To fix this, we are changing the whole tracefs /instances/wifi from
debugfs_tracing_instances to debugfs_wifi_tracing (a few of the files
already had this label).  This simplifies the rules.

Bug: 62413700
Test: Built, flashed, and booted two devices.  Verified that the files
have the correct context and that wifi, camera, and traceur work.

Change-Id: Id62db079f439ae8c531b44d1184eea26d5b760c3