Optimizes `{{#unbound if}}` and `{{#unbound unless}}`.

They no longer create useless metamorph views and generally execute
less code. There is no public API change here, just optimization.

Props to @machty for the review and help.
Merge pull request #3881 from lukemelia/unboundif

Optimizes `{{#unbound if}}` and `{{#unbound unless}}`.