ANDROID: build_config: drop CONFIG_KASAN_PANIC_ON_WARN

CONFIG_KASAN_PANIC_ON_WARN was added in a custom patch for Pixel kernels,
which would make KASAN panic the kernel after the first report regardless
of whether the panic_on_warn parameter is set. (Coincidentally, that patch
also would break instrumentation mode selection for KASAN.)

As that patch was never applied to the common kernel,
CONFIG_KASAN_PANIC_ON_WARN doesn't exist here. This change drops the
non-existent CONFIG_KASAN_PANIC_ON_WARN from build.config.gki_kasan.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Change-Id: I9f42bb5f3515f18e2a5774241ea73a59d8883955