net, lib: kill arch_fast_hash library bits

As there are now no remaining users of arch_fast_hash(), lets kill
it entirely.

This basically reverts commit 71ae8aac3e ("lib: introduce arch
optimized hash library") and follow-up work, that is f.e., commit
237217546d ("lib: hash: follow-up fixups for arch hash"),
commit e3fec2f74f ("lib: Add missing arch generic-y entries for
asm-generic/hash.h") and last but not least commit 6a02652df5
("perf tools: Fix include for non x86 architectures").

Cc: Francesco Fusco <fusco@ntop.org>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/arc/include/asm/Kbuild

@@ -12,7 +12,6 @@ generic-y += fb.h
 generic-y += fcntl.h
 generic-y += ftrace.h
 generic-y += hardirq.h
-generic-y += hash.h
 generic-y += hw_irq.h
 generic-y += ioctl.h
 generic-y += ioctls.h