csky: remove meaningless header-y

Since commit fcc8487d ("uapi: export all headers under uapi
directories"), header-y is meaningless because headers under uapi
are all exported.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Guo Ren <guoren@kernel.org>

arch/csky/include/uapi/asm/Kbuild

 include include/uapi/asm-generic/Kbuild.asm
 
-header-y += cachectl.h
-
 generic-y += auxvec.h
 generic-y += param.h
 generic-y += bpf_perf_event.h