dev-manual: remove qemu machine name list in runqemu invocation

This list of "valid" qemu machine names is obsolete and incorrect, so
just remove it as it serves no real purpose.

(From yocto-docs rev: ee8839480fe574598b4d52a8fd6c11bb301ad3d9)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/qemu.rst

@@ -367,9 +367,6 @@ command line:
 
 -  `VM`: The virtual machine image, which must be a ``.wic.vmdk``
    file. Use this option when you want to boot a ``.wic.vmdk`` image.
-   The image filename you provide must contain one of the following
-   strings: "qemux86-64", "qemux86", "qemuarm", "qemumips64",
-   "qemumips", "qemuppc", or "qemush4".
 
 -  `ROOTFS`: A root filesystem that has one of the following filetype
    extensions: "ext2", "ext3", "ext4", "jffs2", "nfs", or "btrfs". If