Documentation, arch: Remove leftovers from CIFS_WEAK_PW_HASH

This config was removed so remove all references to it.

Fixes: 76a3c92e ("cifs: remove support for NTLM and weaker authentication algorithms")
Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Reviewed-by: Steve French <smfrench@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de> [arch/arm/configs]
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>