TetherController - remove bpf map clears

This action was recently moved into the Tethering mainline module.
As such doing it again here is spurious.

Test: atest, TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I09c3206c06d49a91775a1b5deb72240046f21ee2