logd: Move the capabilities from file based to ambient

This change moves logd's capabilities from being file based to being set
by init through ambient capabilities.

Bug: 62845925
Test: sailfish:/ # grep Cap /proc/`pidof logd`/status
      CapInh: 0000000000000000
      CapPrm: 0000000440000000
      CapEff: 0000000440000000
      CapBnd: 0000000440000040
      CapAmb: 0000000000000000
      $ capsh --decode=0x440000040
      0x440000040=cap_setgid,cap_audit_control,cap_syslog
Test: liblog-unit-tests, logd-unit-tests, logcat-unit-tests
Change-Id: I28c7c4ad37ad5eafd399aef78c303ce31298a9ef