Revert "WifiManager: expose Local Only Hotspot APIs"

This reverts commit ec18f81e.

Reverting the CL to expose the APIs so we have more time for testing
and ironing out the API.

Bug: 31466854
Bug: 37073685
Test: make update-api
Test: make
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Test: frameworks/base/wifi/tests/runtests.sh

Change-Id: I17d4e3e32e28dbbb08ba99c266a9b74044e6001d