docs/system: Remove "mips" board from target-mips.rst

This board had been removed long ago in commit f169413c27
("hw/mips: Remove the 'r4k' machine")

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230202132138.30945-2-jiaxun.yang@flygoat.com>
[PMD: Mention commit f169413c27]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

docs/system/target-mips.rst

@@ -8,8 +8,6 @@ endian options, ``qemu-system-mips``, ``qemu-system-mipsel``
 ``qemu-system-mips64`` and ``qemu-system-mips64el``. Five different
 machine types are emulated:
 
--  A generic ISA PC-like machine \"mips\"
-
 -  The MIPS Malta prototype board \"malta\"
 
 -  An ACER Pica \"pica61\". This machine needs the 64-bit emulator.
@@ -19,18 +17,6 @@ machine types are emulated:
 -  A MIPS Magnum R4000 machine \"magnum\". This machine needs the
    64-bit emulator.
 
-The generic emulation is supported by Debian 'Etch' and is able to
-install Debian into a virtual disk image. The following devices are
-emulated:
-
--  A range of MIPS CPUs, default is the 24Kf
-
--  PC style serial port
-
--  PC style IDE disk
-
--  NE2000 network card
-
 The Malta emulation supports the following devices:
 
 -  Core board with MIPS 24Kf CPU and Galileo system controller