resourceloader: Misc optimisations in startup module

resourceloader: Misc optimisations in startup module

* Remove redundant trackQueue var.
* Simplify logError() code, and remove some local vars.
* Simplify Map#set() code.
* Simplify performance.now check. There are no known browsers,
  supported and unsupported, in which this property is existant
  as anything other than a function.
* Optimised baseModules iteration in sortDependencies().
  Slightly shorter and slightly faster as for-loop.
* Omit trailing dot from error message in one case.
  (None of the other error messages had trailing dots.)
* Add missing space to error message for mainScript.
* Simplify splitModuleKey() code.
* Remove redundant quotes in mw.loader.store.set() for encodedScript.

Differences in response body size on stock MediaWiki.

> uncomp 42152 - 41984 = 168 bytes saved.
> gzip-1 15437 - 15364 =  73 bytes saved.
> gzip-9 13506 - 13419 =  87 bytes saved.

Change-Id: I54c9ab30522c36ece054b915809fe20bff6867b3