Remove mkdocs-material-extensions from requirements.txt (#3666)

The mkdocs-material-extensions package is now deprecated, and it's
usage in mkdocs.yaml was removed in #3663. This fix also removes it
from requirements.txt to prevent unnecessary installation.

Author: gcs278

requirements.txt

@@ -11,7 +11,6 @@ mkdocs==1.6.1
 mkdocs-awesome-pages-plugin==2.10.1
 mkdocs-macros-plugin==1.3.7
 mkdocs-material==9.6.7
-mkdocs-material-extensions==1.3.1
 mkdocs-redirects==1.2.2
 mkdocs-mermaid2-plugin==1.2.1
 pandas>=2.0.3