ANDROID: GKI: remove CONFIG_INIT_STACK_ALL_ZERO from gki_defconfig

Thanks to commit dcb7c0b9 ("hardening: Clarify Kconfig text for
auto-var-init"), CONFIG_INIT_STACK_ALL_ZERO is now automatically
selected depending on the compiler's support for it, so it is not longer
needed to explicitly enable it in the config file.

Fixes: dcb7c0b9 ("hardening: Clarify Kconfig text for auto-var-init")
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I9df386f22d3a24ae0f9ab4da2e0ab35277a48f17