This reverts commit 15f122ee.

Reason for revert: lots of bots are running Powershell 2. the 
new step fails on them (non-fatally though, just generating 
errors in the log, e.g. https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_ng/builds/357219/steps/ensure%20git%20tooling%20on%20windows/logs/stdio)

Original change's description:
> Allow cipd.ps1 execution even if it was fetched from depot_tools.zip.
> 
> Windows keeps track of files downloaded from the Internet and powershell by
> default refuses to execute them (even with RemoteSigned policy). We need to
> explicitly unblock the file first.
> 
> Note: it requires Powershell >= 3.0.
> 
> R=dpranke@chromium.org, iannucci@chromium.org
> BUG=663843
> 
> Change-Id: Id681f4058f906fa4782a360be184d132d837ae78
> Reviewed-on: https://chromium-review.googlesource.com/424327
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
> 

TBR=iannucci@chromium.org,vadimsh@chromium.org,dpranke@chromium.org,chromium-reviews@chromium.org
BUG=663843
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: Ibdc58e60d3f35a760de45bc1f71c88c1c4d2f2df
Reviewed-on: https://chromium-review.googlesource.com/424872
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>