Without this fix, we create a new state-values node for parameters per environment. This is especially bad for heavily branching functions. With the fix, we should only create one node per function.

Drive-by: removes some unused fields for state values in the environment.

BUG=v8:5267

Review-Url: https://codereview.chromium.org/2826223004
Cr-Commit-Position: refs/heads/master@{#44744}