CRM-13072 Remove (deprecated) entity_tag_display as attempting to update...

... the test reveals it has never worked via the api, I don't know what it should do, it's just a v2 hang-over & it is not called directly

Conflicts:

	tests/phpunit/api/v3/EntityTagTest.php

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* CRM-13072: Make PHPunit tests, api functions & BAO functions in the tests standards & E-notice compliant,
  http://issues.civicrm.org/jira/browse/CRM-13072