This removes the libffi.so.6 dependency on Linux.

Bug: 1247674
Change-Id: I271bc6525ffbe8bd413e730b23365e1bc52aa16f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3299731Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Brian Ryner <bryner@google.com>