Remove error hint, no longer relevant

We use TeXLive, where it doesn't occur

README.md

@@ -464,41 +464,6 @@ Hopefully, it spares you some despair.
  delete the `.lua` and `.luc` files of the fonts in question from `luatex-cache/generic/fonts/`.
  For MiKTeX 2.9 on Windows 10, this was found in
  `%USERPROFILE%\AppData\Local\MiKTeX\2.9\luatex-cache`.
-- When using package [`pgf-spectra`](https://ctan.org/pkg/pgf-spectra?lang=en)
- compilation fails with
-
- ```text
- LaTeX Error: File 'spectra.data.tex' not found.
- ```
-
- For a solution, see
- [here](https://tug.org/pipermail/tex-live/2017-January/039591.html), where it says:
-
- > Hi
- >
- > texlive/2016/texmf-dist/tex/latex/pgf-spectra/pgf-spectra.sty
- >
- > ends with
- >
- > \\input{spectra.data.tex}
- >
- > which generates a missing file error if the package is used, the data file
- > is on ctan but it's misplaced in texlive as
- >
- > texlive/2016/texmf-dist/doc/latex/pgf-spectra/spectra.data.tex
- >
- > It should be in the tex tree not doc,
- >
- > David
-
- So, get
- [`spectra.data.tex` from CTAN](http:https://mirrors.ctan.org/graphics/pgf/contrib/pgf-spectra/spectra.data.tex)
- and place it accordingly.
- This can mean placing it in the project root.
- It would be better to put it next to the package file itself, `pgf-spectra.sty`, but this did not
- work even after refreshing the package database.
- This occurred on MiKTeX 2.9.
- TeXLive seemed fine in version 2019.
 - The error is or is similar to:
 
  ```text