Remove mw:Placeholder encapsulation for optional newlines

It seems that the paragraph handler is now smart enough to handle these
newlines more accurately, so this is no longer needed. Removing these newlines
avoids complications in the serializer, and fixes all semantic rt failures in
"1993 NCAA Women's Division I Basketball Tournament". RT testing should
identify problems in the paragraph wrapper, if any.

Change-Id: Ibdb6ad47e2273e7ef2e606a89120d9221bef32f4