Drop the dependency on xtl

[vgvassilev]

We use xtl only for xtl::prefix_path. Let's drop this compile-time dependency.

[mcbarton]

Does this have any relation to this issue #54 ? A PR that fixes this issue should fix the other.

[anutosh491]

Ohh correct yeah. They look related. Is the goal for both the issues same (just curious if there's duplication) ?