Disable grade penalties

[graue]

Until we get better quality data, it might be a net positive to disable grade penalties.

It greatly improves routes along the Polk corridor:

And only slightly worsens a route using the Page Divis hill:

[graue]

This would also fix #117, giving a more direct route that's also less steep and avoids wasted elevation gain:

[graue]

Also removes the sidewalk shortcut in #123.

[graue]

#154 / #155 will fix forward so this isn't necessary