MAINTAINERS: Remove the ipx network layer info

commit <47595e32> ("<MAINTAINERS: Mark some staging directories>")
indicated the ipx network layer as obsolete in Jan 2018,
updated in the MAINTAINERS file.

now, after being exposed for 3 years to refactoring, so to
remove the ipx network layer info from MAINTAINERS.
additionally, there is no module that depends on ipx.h
except a broken staging driver(r8188eu)
Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -9750,11 +9750,6 @@ M:	David Sterba <dsterba@suse.com>
 S:	Odd Fixes
 F:	drivers/tty/ipwireless/
 
-IPX NETWORK LAYER
-L:	netdev@vger.kernel.org
-S:	Obsolete
-F:	include/uapi/linux/ipx.h
-
 IRQ DOMAINS (IRQ NUMBER MAPPING LIBRARY)
 M:	Marc Zyngier <maz@kernel.org>
 S:	Maintained