README: remove Contributions section

The repo is frozen and we are not taking contributions.

Change-Id: I6a2e930427fc03f6c80f3b795bbd77322e1df42e
Reviewed-on: https://go-review.googlesource.com/c/lint/+/625735
Commit-Queue: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>

README.md

diff --git a/README.md b/README.md
index 989b1dc..3edff4f 100644
--- a/README.md
+++ b/README.md
@@ -56,14 +56,6 @@
 [CodeReviewComments](https://golang.org/wiki/CodeReviewComments).
 Changes that are not aligned with those documents will not be considered.
 
-## Contributions
-
-Contributions to this project are welcome provided they are [in scope](#scope),
-though please send mail before starting work on anything major.
-Contributors retain their copyright, so we need you to fill out
-[a short form](https://developers.google.com/open-source/cla/individual)
-before we can accept your contribution.
-
 ## Vim
 
 Add this to your ~/.vimrc: