Fix 1816: Lilypond-book: Give images 1mm less linewidth

Fix 1816: Lilypond-book: Give images 1mm less linewidth

lilypond creates images that are wider than allowed (~0.5-1mm too wide), so
workaround this by removing 1mm from the linewidth.

Also remove code that makes the fragment snippet option imply
ragged-right. Since single-line snippets are now formatted
ragged-right anyway by default in lilypond, we don't need to set
this explicitly. And multi-line snippets are usually not desired
to be printed ragged-right.