chore(internal/kokoro): remove old regen logic (#660)

Fixes: #519

internal/kokoro/synth/sendpr/sendpr.go

diff --git a/internal/kokoro/synth/sendpr/sendpr.go b/internal/kokoro/synth/sendpr/sendpr.go
deleted file mode 100644
index 66ddf3e..0000000
--- a/internal/kokoro/synth/sendpr/sendpr.go
+++ /dev/null
@@ -1,50 +0,0 @@
-// Copyright 2020 Google LLC.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-import (
-	"bytes"
-	"encoding/json"
-	"flag"
-	"io/ioutil"
-	"log"
-	"net/http"
-	"os"
-)
-
-func main() {
-	title := flag.String("title", "", "title for PR")
-	flag.Parse()
-
-	payload := map[string]interface{}{
-		"title": *title,
-		"body":  "", // TODO
-		"head":  "synth-update",
-		"base":  "master",
-	}
-	body, err := json.Marshal(payload)
-	if err != nil {
-		log.Fatal(err)
-	}
-	req, err := http.NewRequest("POST", "https://api.github.com/repos/googleapis/google-api-go-client/pulls", bytes.NewReader(body))
-	if err != nil {
-		log.Fatal(err)
-	}
-	req.Header.Set("Accept", "application/vnd.github.v3+json")
-	req.Header.Set("Authorization", "token "+os.Getenv("GITHUB_TOKEN"))
-
-	resp, err := http.DefaultClient.Do(req)
-	if err != nil {
-		log.Fatal(err)
-	}
-	defer resp.Body.Close()
-
-	bodyBytes, _ := ioutil.ReadAll(resp.Body)
-	if resp.StatusCode > 299 {
-		log.Fatalf("non-OK response creating PR: %s", bodyBytes)
-	}
-
-	log.Printf("PR created: %s", bodyBytes)
-}