powerpc/configs: Drop no longer needed CONFIG_CRYPTO_NULL

Since commit 00b9cfa3 ("mac80111: Add GCMP and GCMP-256 ciphers")
we no longer need to set CONFIG_CRYPTO_NULL in our defconfigs.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/configs/pmac32_defconfig

@@ -309,7 +309,6 @@ CONFIG_XMON=y
 CONFIG_XMON_DEFAULT=y
 CONFIG_BOOTX_TEXT=y
 CONFIG_PPC_EARLY_DEBUG=y
-CONFIG_CRYPTO_NULL=m
 CONFIG_CRYPTO_PCBC=m
 CONFIG_CRYPTO_MD4=m
 CONFIG_CRYPTO_SHA512=m