kbuild: clean up scripts/remove-stale-files

These lines have been here for more than a year. Remove them.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/remove-stale-files

@@ -20,22 +20,4 @@ set -e
 # yard. Stale files stay in this file for a while (for some release cycles?),
 # then will be really dead and removed from the code base entirely.
 
-rm -f arch/powerpc/purgatory/kexec-purgatory.c
-rm -f arch/riscv/purgatory/kexec-purgatory.c
-rm -f arch/x86/purgatory/kexec-purgatory.c
-
-rm -f scripts/extract-cert
-
-rm -f scripts/kconfig/[gmnq]conf-cfg
-
-rm -f rust/target.json
-
-rm -f scripts/bin2c
-
-rm -f .scmversion
-
-rm -rf include/ksym
-
-find . -name '*.usyms' | xargs rm -f
-
 rm -f *.spec