[m-dev.] indent 0 in hlds dumps

[Zoltan Somogyi]

Would anyone object if I removed the Indent arguments
from predicates in hlds_out_*.m where those arguments
only ever contain zero? At the moment, write_hlds itself
is called with an indent of zero from passes_aux.m, and
in a quarter of a century, to the best of my knowledge,
never used any other indent level. Removing all the
do-nothing calls to write_indent would remove some
clutter from the code.

Goals and other structured entities that don't fit on one line
would still be indented, of course.

Zoltan.