binutils: doc: make `make clean` clean more things

binutils: doc: make `make clean` clean more things

There is a bunch of things left over after a `make clean` in the doc
directory.  This patch changes the Makefile so that everything built by
make is cleaned:

- man pages (the man_MANS variable)
- cxxfilt.man
- binutils.info

I am not sure why the last one was in MAINTAINERCLEANFILES.  It's
generated from binutils.texi using makeinfo, and it's not particularly
long to build, so I don't see why it shouldn't be cleaned like the other
files.

Note: with my automake 1,15.1 (built from source), I get a spurious diff
in Makefile.in, where the

  runstatedir = @runstatedir@

line gets removed.  I am not sure why, but I haven't included it.

binutils/ChangeLog:

	* doc/Makefile.am (MOSTLYCLEANFILES): Clean all man pages,
	cxxfilt.man and binutils.info.
	(MAINTAINERCLEANFILES): Remove.
	* doc/Makefile.in: Re-generate.