Drop "depthcharge" and "unified_depthcharge" portage use symbols

We build all firmware with depthcharge now, and all with the same
"unified" configuration, so there's no need for these qualifiers.

TEST=builds still pass

Change-Id: I6ab8a7849d81f7617d5cafb0b423b073e8029c90
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://chromium-review.googlesource.com/406169
Commit-Ready: Patrick Georgi <pgeorgi@chromium.org>
Tested-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
diff --git a/emerge_test.sh b/emerge_test.sh
index 5861aa2..99c33ec 100755
--- a/emerge_test.sh
+++ b/emerge_test.sh
@@ -57,4 +57,4 @@
 # Ignore errors about already working on those repos.
 cros_workon-${BOARD} start ${TEST_EBUILDS} || true
-USE=depthcharge emerge-${BOARD} ${TEST_EBUILDS}
+emerge-${BOARD} ${TEST_EBUILDS}