The hoist_scope member of DeclarationDescriptor was only used to pass the function
scope for declaration of parameters containing sloppy evals, for example:

  function f(x = eval("var y")) { }

In cases like this, "x" is declared in the function scope but "y" is declared in an inner scope.
Rather than passing the function scope as "hoist_scope", we simply ask for the outer_scope()
of the inner scope as needed in PatternRewriter.

This reduces the cognitive overhead of understanding what a DeclarationDescriptor has; for
example, it removes some dead code from the PreParser which never has to deal
with a situation like the example above.

Review-Url: https://codereview.chromium.org/2662183002
Cr-Commit-Position: refs/heads/master@{#42861}