ResourceLoaderStartUpModule: Improve comment about modifiedTime hack
* Re-ordering code to bring the modifiedTime hack and the
loop it serves closer together.
* Separating the fact that it needs a value and the mtime of
startup.js since that is just one of the three factors we use.
This way it's clearer that the startup.js mtime is not just a
bogus value, but not more or less important than wgCacheEpoch
and modules mtime either.
* Remove duplicate '/* Methods */' comment, we already have this
marker a few methods higher up.
Change-Id: Id3a07f02566c0f04b612b81f8353f70fa4ab3977