Only provide default values for required parameters

The test suite already provide optional parameter values for each test
that rely on them, so we do not need to pass them to all tests.

Moreover, some on these changed default values prevent the test suite
from failing because of a regression introduced when refactoring maps.

Remove the default values to trigger the test suite breakage and allow
checking that a fix is working as expected.

spec/defines/resource_map_spec.rb

@@ -15,12 +15,6 @@
       let :default_params do
         {
           string: '$uri',
-          default: 'pool_a',
-          mappings: {
-            'foo' => 'pool_b',
-            'bar' => 'pool_c',
-            'baz' => 'pool_d'
-          }
         }
       end