The condition of a Branch or Select can never be a NumberConstant,
because the resulting graph would be invalid, so we don't need to
optimize this case. It can only ever be a tagged boolean or an untagged
bit.

Drive-by-fix: Test the interesting cases in the unit tests instead.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1195443004

Cr-Commit-Position: refs/heads/master@{#29089}