Delete all *.pyc on update

Last change exhibited issues with stale .pyc files. Let's leave that bake in a
little to cleanup old .pyc files.

TBR=asvitkine@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/8048014

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@102841 0039d316-1c4b-4281-b951-d872f2087c98

update_depot_tools

@@ -94,3 +94,5 @@ then
     echo "Depot Tools has been updated to revision $AFTER_REVISION." 1>&2
   fi
 fi
+
+find . -iname "*.pyc" -delete