Also remove support for "python macros" as the last
existing one is removed in this patch.

Change-Id: I537d604a0a1c9ca11cd5c195841b9f5a0ec74850
Reviewed-on: https://chromium-review.googlesource.com/540836
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Daniel Ehrenberg <littledan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46069}