MAINTAINERS: update staging removals and movements

3 sections have been deleted by various commits.  The other, echo, has
been moved to drivers/misc.

The nominal maintainers of the echo subsystem haven't been modifying the
code or acking/signing patches for several years, so don't keep the
section either.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>