bpf is required - remove checkBpfStatsEnable()

Test: git grep 'nativeGetTotalStat|nativeGetIfaceStat|nativeGetUidStat'
    - shows all locations have been updated
  git grep 'checkBpfStatsEnable'
    - find nothings relevant (just services/art-profile)
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ib584ea57c39d5ab0605787b05133097fd2c82a39