scripts/dtc: dtx_diff: remove broken example from help text

dtx_diff suggests to use <(...) syntax to pipe two inputs into it, but
this has never worked: The /proc/self/fds/... paths passed by the shell
will fail the `[ -f "${dtx}" ] && [ -r "${dtx}" ]` check in compile_to_dts,
but even with this check removed, the function cannot work: hexdump will
eat up the DTB magic, making the subsequent dtc call fail, as a pipe
cannot be rewound.

Simply remove this broken example, as there is already an alternative one
that works fine.

Fixes: 10eadc253d ("dtc: create tool to diff device trees")
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220113081918.10387-1-matthias.schiffer@ew.tq-group.com

scripts/dtc/dtx_diff

@@ -59,12 +59,8 @@ Otherwise DTx is treated as a dts source file (aka .dts).
    or '/include/' to be processed.
 
    If DTx_1 and DTx_2 are in different architectures, then this script
-   may not work since \${ARCH} is part of the include path.  Two possible
-   workarounds:
-
-      `basename $0` \\
-          <(ARCH=arch_of_dtx_1 `basename $0` DTx_1) \\
-          <(ARCH=arch_of_dtx_2 `basename $0` DTx_2)
+   may not work since \${ARCH} is part of the include path.  The following
+   workaround can be used:
 
       `basename $0` ARCH=arch_of_dtx_1 DTx_1 >tmp_dtx_1.dts
       `basename $0` ARCH=arch_of_dtx_2 DTx_2 >tmp_dtx_2.dts