Fix featured `alt` text not being used.

[jkrehm]

Description

Fix featured alt text not being used.

Also:

• Remove comment about old title option for image paths
• Remove unused variables

Motivation and Context

The featured image alt text is not populated even though featuredalt has a value in my blog posts.

Also, the extra variables are confusing, as is the comment about title being an option for image path.

How Has This Been Tested?

I tested with my (very basic) site and with the example site that's bundled with the hugo-future-imperfect theme.

Someone with more Hugo experience (and especially with this template) will hopefully double-check with their site.

Hugo Version:

Hugo Static Site Generator v0.55.5-A83256B9 windows/amd64 BuildDate: 2019-05-02T13:04:07Z

Browser(s):

Firefox

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation, including theme.toml, accordingly.
• [x] I have read the Contributing Document.