Fix warning about generic tracing and eliminate trace from ParsoidConfig.

* Warning about --trace being unsupported was previously being emitted
  even when the --trace flag was not set.
* Warning is now only emitted when the --trace flag is set, but additional
  tracing flags are not provided.
* Removes setting of trace property from setDebuggingFlags in mediawiki.Util.js.
* Removed ParsoidConfig.prototype.trace and any references to
  env.conf.parsoid.trace or parsoidConfig.trace.

Change-Id: Ic3cb384fa0e562654de0679302d453cac49b46ef