Remove reference to ipopt and unpublish unfinished tutorial

docs/reference/externals.md

@@ -194,39 +194,6 @@ misc/test sundials
 
 To install for the current user, run `make install` as usual.
 
-
-### Ipopt
-Another example use of externals is an interface to the constrained Non-Linear
-Program solver [Ipopt](https://coin-or.github.io/Ipopt/). This interface is
-defined in [stdlib/ipopt/ipopt.mc](https://github.com/miking-lang/miking/blob/develop/src/stdlib/ipopt/ipopt.mc) and
-[stdlib/ipopt/ipopt.ext-ocaml.mc](https://github.com/miking-lang/miking/blob/develop/src/stdlib/ipopt/ipopt.ext-ocaml.mc). This library
-depends on both the OCaml library [ipoptml](https://github.com/br4sco/ipoptml)
-and the ipopt c library.
-
-To use this library you need to do the following:
-
-Install the ipopt c library, which you can do on ubuntu 20.04 with
-```
-sudo apt-get install coinor-libipopt-dev
-```
-
-Install dependencies for [ipoptml](https://github.com/br4sco/ipoptml),
-```
-opam install ctypes ctypes-foreign
-```
-
-Clone the [ipoptml](https://github.com/br4sco/ipoptml) repo and in its root run
-```
-dune build
-dune install
-```
-
-You can then test the solver in Miking with
-
-```
-misc/test ipopt
-```
-
 ### External Dependent Utests Pruning
 As part of the parsing (see `prune_external_utests` in `parserutils.ml` for
 details) utests that depend on externals are marked and removed. This done in