Revert "Pin gsutil in cbuildbot."

This reverts CL:172279

Unfortunately we're seeing failures during the build as a
result of this patch.

See http://chromegw/i/chromiumos.tryserver/builders/pre-cq-group/builds/12057

BUG=chromium:305407
TEST=none

Change-Id: I504ad6ea9ab3426fee40d2aee1fce58921188faa
Reviewed-on: https://chromium-review.googlesource.com/175202
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/scripts/deploy_chrome.py b/scripts/deploy_chrome.py
index d24600d..4793c22 100644
--- a/scripts/deploy_chrome.py
+++ b/scripts/deploy_chrome.py
@@ -445,7 +445,7 @@
 
   Returns: Path to the fetched chrome tarball.
   """
-  gs_ctx = gs.GSContext(cache_dir=cache_dir, init_boto=True)
+  gs_ctx = gs.GSContext.Cached(cache_dir, init_boto=True)
   files = gs_ctx.LS(gs_path).output.splitlines()
   files = [found for found in files if
            _UrlBaseName(found).startswith('%s-' % constants.CHROME_PN)]