Set android.hardware.hardware_keystore=400 in C++ insecure impl.

The insecure C++ reference implementation of KeyMint will
not be updated to support versions of the KeyMint HAL newer
than 4. As a result, this implementation should not declare
the newest version of this feature flag, but rather the
latest version it does support.

Bug: 507161881
Test: Treehugger
Flag: EXEMPT BUG_FIX
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:38ca6ba5c09d6ec211e4a7a46b6d906c9f6e9d14
Merged-In: I031e240b022824d15c190525f78ab6624408763c
Change-Id: I031e240b022824d15c190525f78ab6624408763c