[autotest] Use |json| instead of |simplejson|.

simplejson was moved into the library as of python 2.4. We're now at
python 2.6/2.7, and having to keep installing simplejson everywhere has
slowly turned into a hassle.  Since we can just trivially drop/rename
it, let's do so.

The rpc_interface parts of this change have been vetted, the rest is
done just as a s/simplejson/json/ across the code, which afaik should be
a safe thing to do.

BUG=None
TEST=unit, run_suite
DEPLOY=apache

Change-Id: Iab35f71157e7e5cd3be5291c776b07eb3283be8e
Reviewed-on: https://gerrit.chromium.org/gerrit/46424
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Commit-Queue: Aviv Keshet <akeshet@chromium.org>
diff --git a/site_utils/validate_json_files.sh b/site_utils/validate_json_files.sh
index c161a56..a044bb6 100755
--- a/site_utils/validate_json_files.sh
+++ b/site_utils/validate_json_files.sh
@@ -5,9 +5,9 @@
 # found in the LICENSE file.
 
 set -e
-echo "This assumes you have python-simplejson installed"
+echo "This assumes you have python 2.4 or later installed"
 for json in *.json; do
    echo "Validating $json"
-   python -c "import simplejson; simplejson.load(open('$json'))" || \
+   python -c "import json; json.load(open('$json'))" || \
       printf "\n\n$json is broken!!!!\n\n"
 done