misc/git: remove pre-commit file

All hook files are automatically set up when any git-codereview command is run.
And since the contribution guidelines point to installing git-codereview,
this file does not serve any purpose any more.

Change-Id: I165f6905ca03fd3d512c59e2654ef79e76de934c
Reviewed-on: https://go-review.googlesource.com/c/go/+/158677Reviewed-by: Andrew Bonventre <andybons@golang.org>

misc/git/pre-commit

-#!/bin/sh
-# Copyright 2012 The Go Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style
-# license that can be found in the LICENSE file.
-
-# git gofmt pre-commit hook
-#
-# To use, store as .git/hooks/pre-commit inside your repository and make sure
-# it has execute permissions.
-#
-# This script does not handle file names that contain spaces.
-
-gofiles=$(git diff --cached --name-only --diff-filter=ACM | grep '\.go$')
-[ -z "$gofiles" ] && exit 0
-
-unformatted=$(gofmt -l $gofiles)
-[ -z "$unformatted" ] && exit 0
-
-# Some files are not gofmt'd. Print message and fail.
-
-echo >&2 "Go files must be formatted with gofmt. Please run:"
-for fn in $unformatted; do
-	echo >&2 "  gofmt -w $PWD/$fn"
-done
-
-exit 1