libsysutils

Convert the last user to a regular std::vector, and then put List.h out
of its misery.

Turns out there's another copy of this ancient header:
system/core/libutils/include/utils/List.h. This one is included in
various places, but most don't actually use it. There seems to
be a case for a tool to detect unused headers...

Test: m
Change-Id: Ie457bf5e06f6082537f5de2e1fefe7f05a1f0792