Remove cherry-pick-bot config (#59703)

Although not listed on https://killedbygoogle.com/, the Google
cherry-pick bot was killed some time ago and we now use our own bot for
this. Thus we can safely remove the config here.

Also, fixes the shebang in the cherry-pick script.

Release Notes:

- N/A

.github/cherry-pick-bot.yml

@@ -1,2 +0,0 @@
-enabled: true
-preservePullRequestTitle: true

script/cherry-pick

@@ -1,4 +1,4 @@
-# #!/bin/bash
+#!/usr/bin/env bash
 set -euxo pipefail
 
 if [ "$#" -ne 3 ]; then