docs: add missing symbols and remove duplicates from mx-sections.txt
docs: add missing symbols and remove duplicates from mx-sections.txt

jonnylamb/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx,pwithnall/mx,clutter-project/mx,jonnylamb/mx