scripts/kallsyms: remove redundant code for omitting U and N

The symbol types 'U' and 'N' are already filtered out by the following
line in scripts/mksysmap:

    -e ' [aNUw] '

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>