depot_tools: Use system's python for vpython.
depot_tools: Use system's python for vpython.

Using bootstrapped vpython causes problems like [1] when used on
platforms it was not compiled for (e.g. Fedora).

[1] https://chromium-review.googlesource.com/c/infra/infra/+/1929031

Change-Id: I4e62cd1a4e13eee58143695f54ecf80d3473a862
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1930181
Reviewed-by: Anthony Polito <05bb588aa9020353543fee7ac4e6e0a3d0d6f6ed@google.com>
Commit-Queue: Edward Lesmes <d05609f027dc667cc37492b1dc1bdea5d60fa82a@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools