Add the following hook to your theme functions.php file to remove the “Archive for” text from category pages.
add_filter( 'get_the_archive_title', 'artabr_remove_name_cat' );
function artabr_remove_name_cat( $title ){
if ( is_category() ) {
$title = single_cat_title( '', false );
} elseif ( is_tag() ) {
$title = single_tag_title( '', false );
}
return $title;
}