Update xastir to 2.1.8 and update dependencies.

[jasonfenglu]

• Update xastir to 2.1.8
• Beginning from 2.1.8 "./bootstrap.sh" is called to generate configure script.
• Ask for imagemagick 6 explicitly.
• Remove unused dependencies.

[jasonfenglu]

This was tested on Monterey, but I think it also work in Mojave. Maybe #21 is also fixed.