rbconfig_spec.rb: removed needless windows guard
rbconfig_spec.rb: removed needless windows guard

This reverts commit 34b0a7be0ed2fd4ca4d1d509a22964b5e61dfe34.

ruby/spec,nobu/rubyspec,ruby/spec,nobu/rubyspec,nobu/rubyspec,ruby/spec,eregon/rubyspec,eregon/rubyspec,eregon/rubyspec