HLTControlFlowMgr warnings when building the functor cache

The HLTControlFlowMgr prints a couple of warnings when building the functor cache.

HLTControlFlowMgr                   WARNING Unable to locate service "EventSelector"
HLTControlFlowMgr                   WARNING No events will be processed from external input.

These show up as "2 warnings" in the nightly builds. We should whitelist them if they're expected, or fix the cause if not.

(I guess they are "expected" in the sense that the functor cache job doesn't process an input file, but maybe a warning is too severe a level or something.)

/cc @nnolte