Revert "Makefile: optimize generated PDF using Ghostscript"

Temporarily revert, until we can update the GitHub pipeline.

This reverts commit 65bd8e4.

Makefile

@@ -19,7 +19,6 @@ $(PDF_RESULT):
     --require=asciidoctor-mathematical \
     --out-file=$@ \
     $(HEADER_SOURCE)
-	gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/printer -sOutputFile=opt-$@ $@ && mv opt-$@ $@
 
 clean:
 	-rm -f $(SPEC)-*.pdf