[dev.tls] dev.tls: remove sentinel file

Now that we're branched in the history we don't need this anymore.

Change-Id: I0655b2496e273aec87e77557bc4baa06bbc8cfcf
Reviewed-on: https://go-review.googlesource.com/33109
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/dev.tls b/dev.tls
deleted file mode 100644
index 01b05ab..0000000
--- a/dev.tls
+++ /dev/null
@@ -1 +0,0 @@
-Branch for working on TLS 1.3