Removed array_column alias function

The array_column function is only an alias to array_pluck. The alias is not used by Laravel and does not match PHP's spec for array_column. This can cause confusion and also makes it difficult to include the polyfill array_column which is available.

The polyfill function for < PHP 5.5 (from the developer of the native function, matching the spec) is available via Composer at https://github.com/ramsey/array_column.

This is PR #1995 resubmitted on the correct branch (sorry!) and relates to issue #1827.