More StartProfiler.php cleanup

* Now use isset(...) instead of @defined(...) for checking for params.
  As written, &forceprofile simply wouldn't work unless you made it,
  for example, &forceprofile=MEDIAWIKI.
* Removed unnecessary require_once lines.
* Converted to new-style (array-based) profiler config format.
* Removed unnecessary $min and $max args from mt_rand() call.
* Removed uses of the error suppression (@) operator.

Change-Id: I1e394acfb2dd30861d6b5cb55d34f9234cc2d97c
Merge "More StartProfiler.php cleanup"