cmd/vet: fix formatting of headings in doc.go.

This will cause godoc to correctly render these docs,
since go/doc.ToHTML requires no punctuation for headings.

Change-Id: Ic95245147d3585f2ccc59d4424fcab17d2a5617b
Reviewed-on: https://go-review.googlesource.com/31319Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/doc.go

@@ -84,14 +84,14 @@ Flag: -copylocks
 
 Locks that are erroneously passed by value.
 
-Tests, benchmarks and documentation examples
+Tests and documentation examples
 
 Flag: -tests
 
 Mistakes involving tests including functions with incorrect names or signatures
 and example tests that document identifiers not in the package.
 
-Failure to call the cancelation function returned by context.WithCancel.
+Failure to call the cancelation function returned by WithCancel
 
 Flag: -lostcancel
 
@@ -137,8 +137,6 @@ complains about arguments that look like format descriptor strings.
 It also checks for errors such as using a Writer as the first argument of
 Printf.
 
-Struct tags
-
 Range loop variables
 
 Flag: -rangeloops