WifiManager: deprecate and remove setWifiApEnabled

Officially deprecate and remove the setWifiApEnabled call.

Bug: 38436773
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Test: frameworks/base/wifi/tests/runtests.sh
Test: cts-tradefed run cts-dev --mo CtsNetTestCases -t android.net.wifi.cts.WifiManagerTest
Change-Id: Ifefe0b186d074b49ab1cc94e1c166117f3d7bdf7