Remove deprecated extensions code

[ChrisRackauckas]

These have been deprecated for a long time. The ParameterizedFunction one doesn't need to exist anyways because it's just MTK since 2020. So these can just be deleted and that fixes issues like https://github.com/korsbo/Latexify.jl/issues/258

[gustaphe]

I haven't wanted to touch this because I don't know the involved packages. How deprecated are they? Would this be breaking to anyone?

I know these packages were a large part of why @korsbo made Latexify to begin with.

[ChrisRackauckas]

Both are deprecated and have their own Latexify recipes so these not only do nothing, but also throw warnings while doing nothing.

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +10.21 :tada:

Comparison is base (a6c71ef) 72.15% compared to head (2dd069f) 82.36%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #259 +/- ## =========================================== + Coverage 72.15% 82.36% +10.21% =========================================== Files 23 21 -2 Lines 948 828 -120 =========================================== - Hits 684 682 -2 + Misses 264 146 -118 ``` | [Impacted Files](https://codecov.io/gh/korsbo/Latexify.jl/pull/259?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Niklas+Korsbo) | Coverage Δ | | |---|---|---| | [src/Latexify.jl](https://codecov.io/gh/korsbo/Latexify.jl/pull/259?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Niklas+Korsbo#diff-c3JjL0xhdGV4aWZ5Lmps) | `30.76% <ø> (-4.53%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Niklas+Korsbo). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Niklas+Korsbo)

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[korsbo]

This looks fine to me. Thanks 🙂

[KristofferC]

Since this was released as a breaking release, https://github.com/korsbo/Latexify.jl/issues/258 still needs to be fixed since no one will get this release until all packages have upgraded to it.

[korsbo]

aah, right. There's a mismatch between what triggers require (DiffEqBase) and what then gets loaded (ParameterizedFunctions). Should be easy enough to fix.

I still don't mind dropping support for these pretty ancient packages though, so we can let this one stand.