[bootstrap/win] Always use "cipd.bat".

CIPD flags change, and using "cipd.exe" directly skips the selfupdate
step. Remove the optimization and always call "cipd.bat".

BUG=chromium:742448
TEST=None
R=iannucci@chromium.org, sergeyberezin@chromium.org

Change-Id: Ieb353c695a8ef58a51d046f102266d4926a3447c
Reviewed-on: https://chromium-review.googlesource.com/570682
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>

bootstrap/win/win_tools.bat

@@ -44,8 +44,7 @@ if not exist "%WIN_TOOLS_ROOT_DIR%\.bleeding_edge" (
 :: reduces execution time noticeably.
 ::
 :: See "//cipd.bat" and "//cipd.ps1" for more information.
-set CIPD_EXE=%WIN_TOOLS_ROOT_DIR%\.cipd_client.exe
-if not exist "%CIPD_EXE%" set CIPD_EXE=%WIN_TOOLS_ROOT_DIR%\cipd.bat
+set CIPD_EXE=%WIN_TOOLS_ROOT_DIR%\cipd.bat
 set WIN_TOOLS_EXTRA_ARGS=%WIN_TOOLS_EXTRA_ARGS% --cipd-client "%CIPD_EXE%"
 
 :: TODO: This logic will change when we deprecate legacy mode. For now, we