Revert "nix: put builtin in scope when needed"

I don't know where I got this anti-pattern. It makes the LSP unable to
figure out which bindings are unbound

nix/custom/hiosevka/default.nix

@@ -2,7 +2,6 @@
 let
   pname = "hiosevka";
 in
-with builtins;
 (iosevka.overrideAttrs (_: { inherit pname; })).override {
   set = pname;
   /* Guide: https://github.com/be5invis/Iosevka/blob/main/doc/custom-build.md
@@ -10,5 +9,5 @@ with builtins;
      Use `term` spacing to avoid dashed arrow issue
      https://github.com/ryanoasis/nerd-fonts/issues/1018
   */
-  privateBuildPlan = readFile ./buildplan.toml;
+  privateBuildPlan = builtins.readFile ./buildplan.toml;
 }