kbuild: do not remove 'linux' link in scripts/link-vmlinux.sh

arch/um/Makefile passes the -f option to the ln command:

  linux: vmlinux
          @echo '  LINK $@'
          $(Q)ln -f $< $@

So, the hard link is always re-created, and the old one is removed
anyway.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

scripts/link-vmlinux.sh

@@ -206,7 +206,6 @@ vmlinux_link()
 			-Wl,-T,${lds}				\
 			${objects}				\
 			-lutil -lrt -lpthread
-		rm -f linux
 	fi
 }