Remove the tethering hiddenapi whitelist entry

Dexes under /apex are automatically whitelisted.

Bug: 146757305
Test: presubmit
Change-Id: I97af6d911c7e9bafdaa2a97102b2131dea6c0896
Merged-In: I97af6d911c7e9bafdaa2a97102b2131dea6c0896
(cherry picked from commit e11221c7)