Use external dependency for protofiles

The protofiles package installs .proto files for enterprise
support. This patch uses the new external dependency target that
builds them into a static library instead of building them as a part
of libchromeos directly.

CQ-DEPEND=I2298eba02435229b0d0bf00b3afbf30437a99451
BUG=None
TEST=emerge-BOARD platform2

Change-Id: I5a68f426e466c3ab827150410aab8eba669eccf6
Reviewed-on: https://chromium-review.googlesource.com/176607
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Chris Masone <cmasone@chromium.org>
2 files changed