Remove the visit machinery in RealisedPath

In addition to being some ugly template trickery, it was also totally
useless as it was used in only one place where I could replace it by
just a few extra characters

src/libstore/realisation.cc

@@ -47,7 +47,7 @@ Realisation Realisation::fromJSON(
 }
 
 StorePath RealisedPath::path() const {
-    return visit([](auto && arg) { return arg.getPath(); });
+    return std::visit([](auto && arg) { return arg.getPath(); }, raw);
 }
 
 void RealisedPath::closure(

src/libstore/realisation.hh

@@ -58,19 +58,6 @@ struct RealisedPath {
     RealisedPath(StorePath path) : raw(OpaquePath{path}) {}
     RealisedPath(Realisation r) : raw(r) {}
 
-    /**
-     * Syntactic sugar to run `std::visit` on the raw value:
-     * path.visit(blah) == std::visit(blah, path.raw)
-     */
-    template <class Visitor>
-    constexpr decltype(auto) visit(Visitor && vis) {
-        return std::visit(vis, raw);
-    }
-    template <class Visitor>
-    constexpr decltype(auto) visit(Visitor && vis) const {
-        return std::visit(vis, raw);
-    }
-
     /**
      * Get the raw store path associated to this
      */