pp_formline: don't set itemsize in FF_LINEGLOB

pp_formline: don't set itemsize in FF_LINEGLOB

This var is used to enable padding or truncating of output items.
FF_LINESNGL/FF_LINEGLOB do their own version of this, so there's
no need to set it there.

Or to put it another way, we don't expect a FF_LINESNGL or FF_LINEGLOB op
to be followed immediately by FF_SPACE, FF_HALFSPACE, FF_ITEM nor FF_MORE.

Not calculating it makes the code simpler and eases the path to merging
the appending code.