cmd/vet: remove extraneous "//" in dead.go so its comment does not

appear at the top of vet's godoc output

Change-Id: I2593d294b0497aeb9e8c54a4dad052b5c33ecaee
Reviewed-on: https://go-review.googlesource.com/65630
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/dead.go

@@ -4,7 +4,7 @@
 //
 // Simplified dead code detector. Used for skipping certain checks
 // on unreachable code (for instance, shift checks on arch-specific code).
-//
+
 package main
 
 import (