linux-postmarketos-allwinner: unset ANDROID_BINDER_IPC_SELFTEST

Fix long waydroid initialization time.

Related: pmbootstrap#2222 (closed)

This is the only kernel in main and community that had the option enabled.

pmbootstrap patch to add it to kconfig check (to be merged after this MR): https://lists.sr.ht/~postmarketos/pmbootstrap-devel/patches/39960