Remove comments referencing bootstrap.py from base/BUILD.gn

The comments are no longer applicable.

BUG=863460
R=thakis

Change-Id: I29d89d18509f600aeac094fa577ec497377bcb93
Reviewed-on: https://chromium-review.googlesource.com/1142375
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576219}
1 file changed