private_title_format
is a filter applied to the post title when the post visibility is set to private.
/* Removing protected prefix from post titles */
function spi_remove_private_protected_from_titles( $format, $post ) {
return '%s';
}
add_filter( 'private_title_format', 'spi_remove_private_protected_from_titles' );
get_the_title() is located in wp-includes/post-template.php
.