Revert "init.rc: create /data/misc/threadnetwork folder"

This reverts commit 40e1666f.

Reason for revert: this directory is for the Thread stack which is
in the Tethering mainline module. Per mainline guideline, the data
should be saved in a APEX specific directory (i.e.
/data/misc/apexdata/com.android.tethering). It's safe to remove this
directory directly given this is a new feature targeting Android V

Bug: 309932508
Test: manually verified that Thread settings file can be written to
      /data/misc/apexdata/com.android.tethering/threadnetwork
Change-Id: I3a7e24b4cdc1c99ca36a22414507538279dd31cd