WindowInsets: Ignore consumeStableInsets()

With the introduction of insets types we no longer support consuming
individual insets.

Instead we consumed all insets, regardless of whether you consumed
stable or system insets - but that led to compat issues.

On Q, consumeStableInsets was almost always a no-op anyways, because
stable insets already came pre-consumed during dispatch.

This change makes consumeStableInsets() a no-op to more closely match
that behavior.

Bug: 152033222
Test: atest WindowInsetsTest
Change-Id: Ic48ee7386320fc16449ac79435b69305a8132bf8