cleanup - read_config() and ipv4_local_prefixlen

Test:
  git grep 'read_config|ipv4_local_prefixlen|default_pdp_interface'
  comes up empty

Bug: 144730808
Test: atest clatd_test netd_integration_test
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I67b70fe298f69ac51dfbc5daf4078b842fb62808
5 files changed