Remove RETURNS from BFD chew comments

Remove RETURNS from BFD chew comments

When reading the BFD manual, I noticed text like this:

     -- Function: bool bfd_close (bfd *abfd);
	 Close a BFD. If the BFD was open for writing, then pending
	 operations are completed and the file written out and closed.  If
    ...
       *Returns*
    'TRUE' is returned if all is ok, otherwise 'FALSE'.

The *Returns*, like the *Synopsis* in the earlier patch, is
un-info-like.  It's also used inconsistently.

This patch removes all the uses of the RETURNS word and removes it
entirely from the chew scripts.  Now this example reads:

     -- Function: bool bfd_close (bfd *abfd);
	 Close a BFD. If the BFD was open for writing, then pending
	 operations are completed and the file written out and closed.  If
    ...
	 'TRUE' is returned if all is ok, otherwise 'FALSE'.

In a few cases I had to slightly reword the comment.  There were also
a couple of cases where there was redundant text.  In these cases I
just dropped the RETURNS copy.

2023-02-07  Tom Tromey  <tom@tromey.com>

	* bfd.c, cache.c, compress.c, opncls.c: Remove RETURNS from
	documentation comments.
	* doc/doc.str, doc/proto.str (RETURNS): Remove.