public_key_manager: drop unused module

The last user of this module was removed earlier this year in
crrev.com/c/1659436 ("ctest: deprecate payload signing"), so
drop this entirely.

BUG=chromium:872441
TEST=CQ passes

Change-Id: I0342458d421788182574bbf1cfe0dc0cc8433631
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/1808024
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed