tectonic: move to pkgs/by-name

pkgs/tools/typesetting/tectonic/default.nix

···
 /*
   This file provides the `tectonic-unwrapped` package. On the other hand,
-  the `tectonic` package is defined in `./wrapper.nix`, by wrapping
+  the `tectonic` package is defined in `../tectonic/package.nix`, by wrapping
   - [`tectonic-unwrapped`](./default.nix) i.e. this package, and
   - [`biber-for-tectonic`](./biber.nix),
     which provides a compatible version of `biber`.

pkgs/top-level/all-packages.nix

···
 
   tclap_1_4 = callPackage ../development/libraries/tclap/1.4.nix { };
 
-  tectonic = callPackage ../tools/typesetting/tectonic/wrapper.nix { };
-
   tectonic-unwrapped = callPackage ../tools/typesetting/tectonic {
     harfbuzz = harfbuzzFull;
   };