Media gallery: remove “insert into post” button keeping “Insert gallery” button

I solved in this way

add_filter( 'media_view_strings', 'my_media_view_strings');
function my_media_view_strings($strings) {
  if (!current_user_can('edit_theme_options') ){
    $strings["insertMediaTitle"] = ""; //Don't unset!
    unset($strings["insertFromUrlTitle"]);
  }
  return $strings;
}

//Media button click open "Create Gallery"
add_action( 'wp_enqueue_media', 'openGallery' );
function openGallery(){
  if (!current_user_can('edit_theme_options') )
    add_action( 'admin_print_footer_scripts','openGallery_script', 999);
}
function openGallery_script(){
?>
<script type="text/javascript">
jQuery(function(){
  jQuery(".insert-media").click(function (event){
    var options = {
                frame: 'post',
                state: 'gallery',
                title: wp.media.view.l10n.createGalleryTitle,
                multiple: true
        };
        wp.media.editor.open(null,options);
    });
});
</script>';
<?php
}

Now when a contributor click on “Add Media” button, it shows “Create Gallery” interface.

Problem solved! 🙂