Remove “Insert from URL” link in Media upload – WP 3.5

This should work:

add_filter( 'media_view_strings', 'cor_media_view_strings' );
/**
 * Removes the media 'From URL' string.
 *
 * @see wp-includes|media.php
 */
function cor_media_view_strings( $strings ) {
    unset( $strings['insertFromUrlTitle'] );
    return $strings;
}