Removing undesired buttons

By customizing the <ConfluenceInstall>/confluence/decorators/includes/dashboard-navigation.vm is possible to hide the icons you don't want to be shown to the users:

<ul class="ajs-menu-bar">
#menuMacros_renderButton("system.dashboard.button")
</ul>

If you have any doubts regarding customizations, please access Atlassian Answers