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;
}