[vpython] Stop stripping -S from Python invocation
[vpython] Stop stripping -S from Python invocation

The underlying issue that motivated this 1.5 years ago appears to no
longer be a concern (crbug.com/800662). This interferes with code
indexers trying to determine what directories the virtual environment
is providing versus the system. See
https://github.com/microsoft/python-language-server/blob/754a66808005d9849e415ad8d1a2fe2b7edad7c7/src/Analysis/Ast/Impl/get_search_paths.py#L26
for an example.

BUG=chromium:989973
TEST=go test ./...

Change-Id: Ice03afe39a94d47373489a5cf46a29e3b3cd50ce
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1731676
Auto-Submit: Jason Clinton <903dc7ec7b1e0549bc200a3278469a1b3add1d8d@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go