resourceloader: Remove redundant closure of some startup and base files

resourceloader: Remove redundant closure of some startup and base files

* errorLogger: Contains only top-level assignments and statements,
  no scope needed. If it does need a scope at some point, then it
  should be converted to packageFiles first so that the closure
  still isn't needed (see T50886).

* requestIdleCallback: This file should do nothing in modern browsers,
  except alias a native method, and expose the fallback for testing.
  Remove the closure and with it the (usually) unused local var.

* mediawiki.js: Use the shorter Object.hasOwnProperty instead,
  we already do this in several files. Both provide a quick reference
  to the native method. Object.prototype.hasOwnProperty is more direct
  visually, but also less direct at run-time (3 lookups instead of 2).
  MW does not support environments that extend native classes such as
  Object or their prototypes, so this makes no difference in that
  regard and is already done in several core files. (More wide changes
  to be done separately).

Change-Id: I98ed4da4807c54254669053cef47a3e67b4ad2cf