Merge pull request matplotlib#19003 from anntzer/noum

Remove reference to unicode-math in pgf preamble.

Author: timhoffm

lib/matplotlib/backends/backend_pgf.py

@@ -792,9 +792,6 @@ def _print_pgf_to_fh(self, fh, *, bbox_inches_restore=None):
 %% Make sure the required packages are loaded in your preamble
 %%   \\usepackage{pgf}
 %%
-%% and on luatex and xetex
-%%   \\usepackage{unicode-math}
-%%
 %% Figures using additional raster images can only be included by \\input if
 %% they are in the same directory as the main LaTeX file. For loading figures
 %% from other directories you can use the `import` package