adbd: remove ifdefs guarding root/secure.

The same adbd module prebuilt will get used for both user and userdebug
builds in the post-APEX world, so we can't guard functionality with
product variable ifdefs anymore.

The code that was previously compiled out runs before we drop root, so
the increased attack surface essentially consists of an attacker having
control over system properties, and that likely implies that we're
doomed already (either they have filesystem control, or they have code
execution in init).

Bug: http://b/158156979
Test: treehugger
Change-Id: Ia70d3140189e5212beb813ff719355e30ca5fa04
(cherry picked from commit d076857c)