chore(build): Don't clean the book before building.

Not sure why I added this in the first place, thanks @mguichard for pointing it out. The only scenario where this causes issues is locally, since CI uses a fresh repo copy.

build-book.sh

@@ -6,7 +6,6 @@ START_SERVER=${1:-false}
 PAGE_ROOT=${2:-"/"}
 
 # Build the jupyter book, everything else is post-processing
-jupyter-book clean book/
 jupyter-book build book/
 
 # Note: the structure of thebe_lite mimicks where thing are needed in the html folder
@@ -55,4 +54,4 @@ else
 fi
 
 echo "To close a python server run the commeand:
-	kill-server.sh"
\ No newline at end of file
+	kill-server.sh"