Removed prelude::* from libstd files.

This replaces the imports from the prelude with the re-exported symbols.
Added missing Windows/Mac OS X import.
Cleaned up a lint warning.
auto merge of #12006 : chromatic/rust/gh_11983_deglob_std, r=brson

This replaces the imports from the prelude with the re-exported symbols, as requested in #11983.