Hello,
you have probably modified the login template after having install Social Login 3.5. This is why it was not correctly removed when you uninstalled it now.
In your theme directory you need to open Login.template.php. There you need to remove this block:
<p style="text-align:left;">
<div class="oneall_social_login_providers" id="oneall_social_login_providers_', $rand, '"></div>
<script type="text/javascript">
oneall.api.plugins.social_login.build("oneall_social_login_providers_', $rand, '", {
"providers": [\'', implode ("', '", $providers), '\'],
"callback_uri": \'', $boardurl, '/index.php?action=oasl_callback;oasl_source=login\',
});
</script>
<!-- OneAll.com / Social Login for SMF -->
</p>