Update mixins.json

Removing BTO and AMAD from the reg-ex for biosample_term_id
Update biosample.json
Update biosample.json

Removing BTO from the test set
Update experiment.json

Removing BTO from the test data
Merge pull request #298 from ENCODE-DCC/1516-No_more_BTO

1516 no more bto
Merge remote-tracking branch 'origin/master' into 52_file_viz