Remove sans-serif ebook hacks

Those are not needed anymore.
- Symbolic links
- Update .gitignore files

.gitignore

@@ -12,53 +12,31 @@
 *.run.xml
 *.html
 *.dlog
+*.bak
+*.opf
 book/book.out
 .vscode/
-book/book.synctex*
-book/tikz-cache/*
 book/bookch*
-book/content.opf
-book/output-epub
 book/figures/*.png
 book/figures/*.pdf
 book/figures/*.in
-book/tables/*.png
-book/tables/*.pdf
-book/release/*
 book/book*.4ct
 book/book*.4tc
-book/book*.aux
-book/book*.bbl
-book/book*.bcf
-book/book*.blg
 book/book*.css
 book/book*.dvi
-book/book*.html
 book/book*.idv
 book/book*.lg
-book/book*.log
-book/book*.mobi
-book/book*.azw3
-book/book*.epub
 book/book*.ncx
 book/book*.out
-book/book*.pdf
-book/book*.run.xml
 book/book*.tmp
-book/book*.toc
 book/book*.xref
-book/book*.html
 book/book*.svg
-book/book-epub/
-book/book-mobi/
-book/book-azw3/
-*.bak
-book_sans_serif/
-book_serif/
-release_sans_serif/
-book/book_sans_serif-epub/
+# Directories created during build
+book/book_sans_serif/*
+book/book_serif/*
 book/static_website_html/*
+book/website/static_website_html/*
+book/epub/
+book/book-epub/
 book/bw-book-epub/*
-epub/
-*.opf
-website/static_website_html/*
+book/release/*

book/book_sans_serif.tex

@@ -1,4 +1,2 @@
 \def\isaccessible{1}
-% We have to use a symlink to book.tex to prevent tex4ebook to load book.ht4
-% before loading any other package and create conflicts 
-\input{sourdough_book.tex}
+\input{book.tex}

book/sourdough_book.tex

@@ -1 +0,0 @@
-book.tex