Remove the recently-added dependency on the truncate program for
building the kernel. truncate is not available when building the kernel
under Yocto. It could be added, but it would be better just to avoid
the unnecessary dependency.

Fixes: 1472464c

 ("kbuild: avoid scripts/kallsyms parsing /dev/null")
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>