parisc: remove arch/parisc/nm

Parisc overrides 'nm' with a shell script. I was hit by a false-positive
error of $(NM) because this script returns the exit status of grep
instead of ${CROSS_COMPILE}nm. (grep returns 1 if no lines were selected)

I tried to fix it, but in the code review, Helge suggested to remove it
entirely. [1]

This script was added in 2003. [2]

Presumably, it was a workaround for old toolchains (but even the parisc
maintainer does not know the detail any more).

Hopefully, recent tools should work fine.

[1]: https://lore.kernel.org/all/1c12cd26-d8aa-4498-f4c0-29478b9578fe@gmx.de/
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=36eaa6e4c0e0b6950136b956b72fd08155b92ca3



Suggested-by: Helge Deller <deller@gmx.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Helge Deller <deller@gmx.de>