you can write custom clientlib where you can define the logic of hiding the targetting button.
Example :
(function($, window) {
'use strict';
/* editor panel selector */
var headerSelector = '.editor-GlobalBar.editor-panel-header .header-main';
/* targeting mode selector */
var targetingLayer = '#selectlayer-popover .js-editor-LayerSwitcherTrigger[data-layer="Targeting"]';
$(window.document).ready( function() {
var header = $(headerSelector);
/* wait until content frame is loaded */
$(window.document).on('click', '[href="#selectlayer-popover"]', function() {
/* hide targeting layer */
header.find(targetingLayer).hide();
});
});
}(jQuery, window));