Youzify - BuddyPress Disable Posting form on Global Activity Stream.

yzc_disable_activity_stream_wall_form.php

<?php

/**
* Youzify - BuddyPress Disable Posting form on Global Activity Stream.
*/
function yzc_disable_activity_stream_wall_form( $enable ) {

    if ( bp_is_active( 'activity' ) && bp_is_activity_directory() ) {
        return false;
    }

    return $enable;
}
add_filter( 'youzify_is_wall_posting_form_active', 'yzc_disable_activity_stream_wall_form' );