(maint) remove duplicate code from resolution test

Prior to this commit, the tests for Facter::Util::Resolution were the
same for windows and non-windows systems. This commit combines those two
tests.
(maint) remove unused code from resolution_spec

Prior to this commit, the resolution_spec.rb file tests setcode for both
a windows and non-windows system. The tests come out exactly the same
for both systems. An investigation into the code suggests that this
platform distinction is never actually used. This commit removes the
part of the test that specifies what to do on a windows vs. non-windows
system.
Merge pull request #452 from melissaanne/maint/master/remove_duplication_from_resolution_tests

(maint) remove duplicate code from resolution test