internal/history: delete duplicate package comment

CL 296429 added history.go with a package comment even though there
was one in release.go. Drop one of the two, keeping one that sounds
slightly better and is located in the more typical place-a .go file
whose name is the same as the package name.

Change-Id: I31ab5ee4bc9fa02aaf98c0d399ae7d212f1fd2bc
Reviewed-on: https://go-review.googlesource.com/c/website/+/473236
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Rhys Hiltner <rhys.hiltner@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

internal/history/release.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package history stores historical data for the Go project.
 package history
 
 import "html/template"