Re-Revert "Enable tethering namespace accessible in Android native level."

This reverts commit 32bd9d6d.

Reason for revert: Original commit was for native experiment setup.
But SEPolicy was not updated and sync to native level always fail in T devices.
This CL will clean up incomplete native experiment setup.
Even if we decide that we want to use flags from native code in the Tethering module,
we will do so using a new namespace, tethering_u_plus_native.

Re-applying the revert as it was not applied to downstream branches,
and ended up being lost when they were promoted back to
aosp-master.

Test: m
Bug: 264947218
(cherry picked from commit 78ef4714)

Change-Id: I67b914e15a5e149cc608bb37b9d09ed154b58dba