enable formatting for samples

Author: louis-bompart

.prettierignore

@@ -8,8 +8,5 @@ package-lock.json
 /packages/lit-dev-content/_dev/
 /packages/lit-dev-content/_site/
 /packages/lit-dev-content/rollupout/
-# TODO(aomarks) Would be nice to format samples, but Prettier doesn't always do
-# a great job compared to our manual formatting.
-/packages/lit-dev-content/samples/
 
 .wireit