Convert tests to use plain rspec-puppet

Tests in the new style produces the following documentation output:

abs
  should not eq nil
  should run abs() and raise an Puppet::ParseError
  should run abs(-34) and return 34
  should run abs("-34") and return 34
  should run abs(34) and return 34
  should run abs("34") and return 34

1 files changed, 1 insertions, 4 deletions

diff --git a/spec/functions/strftime_spec.rb b/spec/functions/strftime_spec.rb
index ebec54b..e76774a 100755
--- a/spec/functions/strftime_spec.rb
+++ b/spec/functions/strftime_spec.rb
@@ -1,9 +1,6 @@
-#! /usr/bin/env ruby -S rspec
 require 'spec_helper'
 
-describe "the strftime function" do
-  let(:scope) { PuppetlabsSpec::PuppetInternals.scope }
-
+describe 'strftime' do
   it "should exist" do
     expect(Puppet::Parser::Functions.function("strftime")).to eq("function_strftime")
   end