replace dead my_fixture_read method

this was previously provided by puppetlabs_spec_helper, which we don't
use anymore.

Author: bastelfreak

spec/unit/puppet/provider/package/npm_spec.rb

@@ -66,7 +66,7 @@ def self.it_should_respond_to(*actions)
     it 'returns a list of npm packages installed globally' do
       provider.class.expects(:execute).
         with(['/usr/local/bin/npm', 'list', '--json', '--global'], anything).
-        returns(Puppet::Util::Execution::ProcessOutput.new(my_fixture_read('npm_global'), 0))
+        returns(Puppet::Util::Execution::ProcessOutput.new(File.read('spec/fixtures/unit/puppet/provider/package/npm/npm_global'), 0))
       expect(provider.class.instances.map(&:properties).sort_by { |res| res[:name] }).to eq([
                                                                                               { ensure: '2.5.9', provider: 'npm', name: 'express' },
                                                                                               { ensure: '1.1.15', provider: 'npm', name: 'npm' }
@@ -76,7 +76,7 @@ def self.it_should_respond_to(*actions)
     it 'logs and continue if the list command has a non-zero exit code' do
       provider.class.expects(:execute).
         with(['/usr/local/bin/npm', 'list', '--json', '--global'], anything).
-        returns(Puppet::Util::Execution::ProcessOutput.new(my_fixture_read('npm_global'), 123))
+        returns(Puppet::Util::Execution::ProcessOutput.new(File.read('spec/fixtures/unit/puppet/provider/package/npm/npm_global'), 123))
       Puppet.expects(:debug).with(regexp_matches(%r{123}))
       expect(provider.class.instances.map(&:properties)).not_to eq([])
     end