Revert "fix 2 xml errors in the description of boot.loader.grub.efiInstallAsRemovable"

This reverts commit 656cc3ac because it
causes building the manual to fail:

  $ nixos-rebuild build
  ...
  building path(s) ‘/nix/store/s9y5z78z5pssvmixcmv9ix13gs8xj87f-manual-olinkdb’
  Writing /nix/store/s9y5z78z5pssvmixcmv9ix13gs8xj87f-manual-olinkdb/manual.db for book(book-nixos-manual)
  ./man-pages.xml:625: element para: Relax-NG validity error : Did not expect element para there
  ./man-pages.xml:3: element variablelist: Relax-NG validity error : Element refsection has extra content: variablelist
  ./man-pages.xml:29: element refsection: Relax-NG validity error : Element refentry has extra content: refsection
  ./man-pages.xml:3: element reference: Relax-NG validity error : Element reference failed to validate content
  ./man-pages.xml fails to validate

CC @cleverca22, @Mic92