Clean up example a little (#89)

## Summary:
I realized:
- it's simpler to avoid the usual `cmd` and just put it all in the same
  directory
- we don't need schema.json since GitHub now posts a schema in SDL
  format

## Test plan:
make lint example


Author: benjaminjkraft

Reviewers: dnerdy, StevenACoffman, aberkan, jvoll, mahtabsabet, MiguelCastillo

Required Reviewers: 

Approved By: dnerdy, StevenACoffman

Checks: ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Lint, ✅ Test (1.17), ✅ Test (1.16), ✅ Test (1.15), ✅ Test (1.14), ✅ Lint

Pull Request URL: https://github.com/Khan/genqlient/pull/89

generate/example_test.go

@@ -18,7 +18,7 @@ func TestRunExample(t *testing.T) {
 		t.Skip("requires GITHUB_TOKEN to be set")
 	}
 
-	cmd := exec.Command("go", "run", "./example/cmd/example", "benjaminjkraft")
+	cmd := exec.Command("go", "run", "./example", "benjaminjkraft")
 	cmd.Dir = integration.RepoRoot(t)
 	out, err := cmd.CombinedOutput()
 	if err != nil {