This removes unused code (macros.py, runtime functions). As IS_VAR is
now unused we can remove support from the parser.

Bug: v8:7624
Change-Id: Ia1c5e23f4c2caa85310d3f9a557218fc52d200f2
Reviewed-on: https://chromium-review.googlesource.com/c/1329696Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57434}