Update _config.yml (#17)

Author: tshiya731

book/_config.yml

@@ -15,10 +15,6 @@ latex:
   latex_documents:
     targetname: book.tex
 
-parse:
-  myst_enable_extensions:
-    - citations
-
 # Add a bibtex file so that we can create citations
 bibtex_bibfiles:
   - references.bib
@@ -59,6 +55,5 @@ sphinx:
   extra_extensions:
     - sphinx.ext.imgconverter
     - download_link_replacer
-    - sphinxcontrib.bibtex
     - jupyterbook_patches