Partial: Reland "libbinder: remove __ANDROID_APEX__ stability diff"

This is a piece of a CL that landed internally, moved to AOSP to avoid
merge conflicts.

Since the product partition is using __ANDROID_VNDK__, we can't remove
the __ANDROID_APEX__ check from the NDK header.

This reverts commit 15b70298.

Reason for revert: reland b/179906909

Fixes: 179906909
Test: the following, which was failing before w/ stability error
mmma packages/modules/Gki
adb install --staged-ready-timeout 600000\
   out/host/linux-x86/testcases/GkiInstallTest/com.android.gki.kmi_5_10_android12_0_test_high.apex

Merged-In: I189b5c07ffd767fa46c59fd8828ba4f59b31f095
Change-Id: I27231c4f0a5f8c1b745ee722daa1337026fc3b2a