Remove change_ota_channel_pref.sh
fix #247
close #257
Merge pull request #258 from askeing/remove_old_script

Remove change_ota_channel_pref.sh
Added NO_FTU environment support
 - set up NO_FTU=true for no ftu.
Merge pull request #259 from askeing/NO_FTU

Added NO_FTU environment support