This function had been marked as deprecated.

Legacy function used to generate the categories checklist control.

Signature

dropdown_categories( $default = 0, $parent = 0, $popular_ids = array() )
default
 (int) Unused.
Default: 0
parent
 (int) Unused.
Default: 0
popular_ids
 (array) Unused.
Default: array()

Return

(void)

Source

function dropdown_categories( $default = 0, $parent = 0, $popular_ids = array() ) {
	_deprecated_function( __FUNCTION__, '2.6.0', 'wp_category_checklist()' );
	global $post_ID;
	wp_category_checklist( $post_ID );
}
WP Trac GitHub

Link here