Move wifi related hidden API flag file entries to packages/modules/Wifi

Bug: 179354495
Test: m com.android.wifi
      - ensure that the generated APEX is byte-for-byte identical
        before and after these changes.
      m out/soong/hiddenapi/hiddenapi-flags.csv
      - make sure that they are not changed by this.
Change-Id: I45f46f9aebb90ca9ff0a60c37068b94238354578