wordpress: modify admin panel post section items

gistfile1

/*
Plugin Name: Admin mods
Description: This plugin removes unwanted items from wordpress admin panel
Version: 1.0
Author: Ankit Agrawal
*/

//function to add custom coloumns
add_filter( 'manage_edit-post_columns', 'my_columns_filter', 10, 1 );
add_action( 'manage_posts_custom_column', 'my_column_action', 10, 1 );
//add_filter("manage_edit-post_sortable_columns", 'my_columns_sort');
function my_columns_filter( $columns ) {
	$column_thumbnail = array( 'media' => 'Media Type' );

	$columns = array_slice( $columns, 0, 5, true ) + $column_thumbnail + array_slice( $columns, 1, NULL, true );

	return $columns;
}

function my_column_action( $column ) {
	global $post;
	switch ( $column ) {
		case 'media':
			echo  get_content_type_by_post_id($post->ID);
			break;
	}
}

// function to get content type in posts
function get_content_type_by_post_id($postid)
{
	$metaarr=get_post_meta($postid);
	if($metaarr['content_type'][0]=='image')
	{
		$content_type="Image";
	}
	if($metaarr['content_type'][0]=='video')
	{
		$content_type="Video";
	}
	if($metaarr['content_type'][0]=='mixed')
	{
		$content_type="Image/Video";
	}
	if($metaarr['content_type'][0]=='text')
	{
		$content_type="Text/Image";
	}
	if($metaarr['content_type'][0]=='patti')
	{
		$content_type="Patti";
	}
	return $content_type;
}

//remove update messages
add_action('admin_menu','wphidenag');
function wphidenag() {
remove_action( 'admin_notices', 'update_nag', 3 );
}