rm update_llvm.sh (it's legacy) (#1351)

third_party/update_llvm.sh

@@ -1,19 +0,0 @@
-#!/bin/bash -eux
-# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-# Exceptions. See /LICENSE for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-# Ensure the working directory is the script's directory.
-cd "$(dirname "$0")"
-
-# Update the `llvm-bazel` project first by just pulling from its HEAD.
-git submodule update --remote llvm-bazel
-
-# Find the current LLVM commit in the `llvm-bazel` project.
-llvm_commit=$(cd llvm-bazel; git submodule status third_party/llvm-project | awk '/-[0-9a-f]+ / { print substr($1, 2) }')
-
-# Fetch and checkout this commit of LLVM
-cd llvm-project
-git fetch
-git checkout $llvm_commit
-cd ..