[release-branch.go1.13] crypto/tls: make SSLv3 again disabled by default

It was mistakenly re-enabled in CL 146217.

Updates #33837

Change-Id: I8c0e1787114c6232df5888e51e355906622295bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/191877


Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
(cherry picked from commit 2ebc3d81)
Reviewed-on: https://go-review.googlesource.com/c/go/+/191998