Stop emitting warning on missing nose files

OpenStack, with one exception, uses testr to run its tests. That means
that the expected outcome of run_tox.sh is that there is no
nose_results.html - however we emit a warning about it being missing on
every run. For folks less familiar with our systems trying to debug test
failures, it's a line that could confuse them.

Change-Id: I60f6b1f1e49bb8b001d5e9743273830188b150f1

jenkins/scripts/run-tox.sh

@@ -103,10 +103,6 @@ function check_nose_html {
             echo
             exit 1
         fi
-    else
-        echo
-        echo "WARNING: Unable to find $NOSE_HTML_OUT_FILE to confirm results!"
-        echo
     fi
 }