Remove unused template_id from controlled vocabularies

[kdp-cloud]

The sample_controlled_vocabs table in the schema has an unused template_id field which is not being used in any of our SEEK instances.

SampleControlledVocab.select {|scv| !scv.template_id.nil?}
  SampleControlledVocab Load (0.3ms)  SELECT "sample_controlled_vocabs".* FROM "sample_controlled_vocabs"
 => []

Instead the relation to the template should be made through the template attributes, similar to how it's done for sample types.