CHROMIUM: crypto: Remove obsolete comment about Scoped X509 types

CL:1764236 has now explicitly added ScopedX509 and ScopedNETSCAPE_SPKI
to libchrome crypto/ because these are used in several places in
platform2/.

BUG=chromium:737942
TEST=none

Change-Id: I49d0716514615aea2a3b9c8d46a0e5ac4080714d