Remove guava dependency from testing-common

[laurit]

We don't use guava much so might as well only add the guava dependency to tests that need it. Most of the remaining guava usages are for ImmutableMap.of(). Multi element ImmutableMap.of()

  private static final ImmutableMap<String, String> testHashMap =
      ImmutableMap.of(
          "firstname", "John",
          "lastname", "Doe",
          "age", "53");

could be replaced with

  private static final Map<String, String> testHashMap =
      new HashMap<String, String>() {
        {
          put("firstname", "John");
          put("lastname", "Doe");
          put("age", "53");
        }
      };

if we want to get rid of these too.