ANDROID: gki_defconfig: disable CONFIG_CRYPTO_MD4

The MD4 algorithm is heavily broken and obsolete, and there seems to be
no reason for it to be enabled in GKI.  It originally got enabled at
partner request alongside many other options with the rationale that
they changed the kernel ABI, so they needed to be enabled in GKI for any
module to use it.  But that doesn't apply to MD4 because it doesn't
change the kernel ABI.  Nor should any module be using MD4 anyway.

So let's disable MD4 again.

Bug: 135666008
Bug: 150302692
Change-Id: Iec0946984c4e58bffeab7888e689af035cdd512b
Signed-off-by: Eric Biggers <ebiggers@google.com>