// REMOVE META BOXES FROM DEFAULT POSTS SCREEN
function remove_default_post_screen_metaboxes() {
    remove_meta_box( 'postcustom','post','normal' ); // Custom Fields Metabox
    remove_meta_box( 'postexcerpt','post','normal' ); // Excerpt Metabox
    remove_meta_box( 'commentstatusdiv','post','normal' ); // Comments Metabox
    remove_meta_box( 'trackbacksdiv','post','normal' ); // Talkback Metabox
    remove_meta_box( 'slugdiv','post','normal' ); // Slug Metabox
    remove_meta_box( 'authordiv','post','normal' ); // Author Metabox
}
add_action('admin_menu', 'remove_default_post_screen_metaboxes');


// REMOVE META BOXES FROM DEFAULT PAGES SCREEN
function remove_default_page_screen_metaboxes() {
    remove_meta_box( 'postcustom','page','normal' ); // Custom Fields Metabox
    remove_meta_box( 'postexcerpt','page','normal' ); // Excerpt Metabox
    remove_meta_box( 'commentstatusdiv','page','normal' ); // Comments Metabox
    remove_meta_box( 'trackbacksdiv','page','normal' ); // Talkback Metabox
    remove_meta_box( 'slugdiv','page','normal' ); // Slug Metabox
    remove_meta_box( 'authordiv','page','normal' ); // Author Metabox
}
add_action('admin_menu', 'remove_default_page_screen_metaboxes');