Revert "Make default parser keep comments"

This reverts commit 238899faacc9fae8a31099153b44713bdb6beabb.
Revert "don't remove comments from xml module"

This reverts commit 343456e31445d471492bbfe2d786375ef05352ce.
Merge pull request #1098 from edx/jkarni/fix/revert-xml-comments