samsung: Temporarily disable plugin for Samsung Y3300/Y3400 modems.

There are changes to the broadband bearer code [1] in upstream
ModemManager that requires modifying the Samsung plugin code to be
compatible. This CL temporarily disables the Samsung plugin in order to
pull changes from upstream.

[1] http://cgit.freedesktop.org/ModemManager/ModemManager/commit/?id=caeeae27219a91384fa41ac5a1e0f21e1edbaa76

BUG=chromium-os:30744
TEST=Build modemmanager-next

Change-Id: I53c6e944f6d56276cfd1c54b5cc23a0eac1812ee