install_dependencies: Drop libart dependency for Arch Linux

Hello there, this is my first MR to inkscape :)

libart-lglp¹ is not available at the official Arch Linux repository, and thus, pacman will fail to install all packages listed in that section. Drop the requirement to install it, since it's possible to compile and succeed in all tests without it.

Since I was able to compile, test (100% tests passed, 0 tests failed out of 276 using make check) and run without it, should I drop this dependence for all distros? I didn't find it in the Tracking Dependencies page as well.

Thanks!

1. https://repology.org/project/libart-lgpl/versions (Note that is only available in AUR, where pacman can't access) ↩