[REF] Remove columnName field

[eileenmcnaughton]

Overview

Removes an unnecessary parameter

Before

Parameter in use

After

Parameter gone

Technical Details

This field always holds the same information as ['column_name']. It was introduced
before https://github.com/civicrm/civicrm-core/pull/1206/files which removed some of it's
use but not the variable. There is test coverage on passing in column_name
in testCreateCustomFieldColumnName

Comments

[civibot]

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[colemanw]

Code looks like straightforward cleanup and tests pass.