class PasteAsPlainText {

    function __construct() {

        add_action( 'admin_init', array( $this, 'init' ) );

    }

    function init() {

        add_filter( 'tiny_mce_before_init', array( $this, 'forcePasteAsPlainText' ) );
        add_filter( 'teeny_mce_before_init', array( $this, 'forcePasteAsPlainText' ) );
        add_filter( 'teeny_mce_plugins', array( $this, 'loadPasteInTeeny' ) );
        add_filter( 'mce_buttons_2', array( $this, 'removePasteAsPlainTextButton' ) );

    }

    function forcePasteAsPlainText( $mceInit ) {

        global $tinymce_version;

        if ( $tinymce_version[0] < 4 ) {
            $mceInit[ 'paste_text_sticky' ] = true;
            $mceInit[ 'paste_text_sticky_default' ] = true;
        } else {
            $mceInit[ 'paste_as_text' ] = true;
        }

        return $mceInit;
    }

    function loadPasteInTeeny( $plugins ) {

        return array_merge( $plugins, (array) 'paste' );

    }

    function removePasteAsPlainTextButton( $buttons ) {

        if( ( $key = array_search( 'pastetext', $buttons ) ) !== false ) {
            unset( $buttons[ $key ] );
        }

        return $buttons;

    }

}

new PasteAsPlainText();

function formatTinyMCE( $in ) {
    $in['toolbar1'] = 'bold,custom_em,blockquote,aligncenter,link,unlink,spellchecker,undo,removeformat';
    return $in;
}
add_filter( 'tiny_mce_before_init', 'formatTinyMCE' );