LDC-519 Removed all references to field_tag base field definition.

## Ready State: Yes

JIRA Ticket: https://imagex.atlassian.net/browse/LDC-519

There was a mistake in this component that was referencing the wrong base field. Formerly, it was referencing field_tag, but this has now been corrected to reference the Vocabulary Tags component's base field 'field_tags'. I removed the base field altogether, as it would conflict with its dependancy ImageX Vocabulary Tags module should it be included.

## Requirements & Dependencies

* Imagex Vocabulary Terms module / ImageX InstallKit

## Deployment Instructions

* Merge code.
* Clear all caches

## Usage/Test Instructions

* Check the feature imagex_events to ensure that the correct base field (field_tags) is being referenced and that the erroneous field_tag is not being defined or referenced.