symbolic-ref, update-ref: do not refuse reflog message with LF

symbolic-ref, update-ref: do not refuse reflog message with LF

Earlier these tools refused to create a reflog entry when the
message given by the calling Porcelain had a LF in it, partially
to keep the file format integrity of reflog file, which is
one-entry-per-line.  These tools should not be dictating such a
policy.

Instead, let the codepath to write out the reflog entry worry
about the format integrity and allow messages with LF in them.

Signed-off-by: Junio C Hamano <gitster@pobox.com>