Form actions aren't properly altered to http/https when the site is installed in a subdirectory

With the patch from 🐛 DrupalWebTestCase->getAbsoluteUrl should use internal browser's base URL Postponed: needs info applied and running Drupal at the server root (e.g., http://drupal.dev), I get three test failures in the Secure Pages test suite. However, when running Drupal in a subdirectory (e.g., http://localhost/drupal), I get five failures.

It looks like this is due to a bug where form actions aren't properly being altered to http/https in this case. There is some code in securepages_can_alter_url() that tries to play around with $base_path and $base_url, and that's what's causing it. For the life of me I can't figure out what that code is trying to do, but I'm pretty sure it's unnecessary, and it's definitely broken. The attached patch removes it.

Applying this patch results in consistent test behavior regardless of whether the site is installed in a subdirectory (3 failures either way).