Remove unused Makefile.

metrics is now part of platform2 and built using gyp.

BUG=chromium:342154
TEST=Trybot runs on x86-mario,lumpy,daisy paladin and release builders.

Change-Id: I69c5622399cab9d8508dc75310972ae638f0cac7
Reviewed-on: https://chromium-review.googlesource.com/186194


Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>