regexp: simplify BenchmarkCompileOnepass

One benchmark is fine.
Having one per test case is overkill.

Change-Id: Id4ce789484dab1e79026bdd23cbcd63b2eaceb3f
Reviewed-on: https://go-review.googlesource.com/c/139777
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/regexp/onepass_test.go

@@ -227,21 +227,11 @@ func TestRunOnePass(t *testing.T) {
 }
 
 func BenchmarkCompileOnepass(b *testing.B) {
-	for _, test := range onePassTests {
-		if test.onePass == notOnePass {
-			continue
-		}
-		name := test.re
-		if len(name) > 20 {
-			name = name[:20] + "..."
-		}
-		b.Run(name, func(b *testing.B) {
 	b.ReportAllocs()
+	const re = `^a.[l-nA-Cg-j]?e$`
 	for i := 0; i < b.N; i++ {
-				if _, err := Compile(test.re); err != nil {
+		if _, err := Compile(re); err != nil {
 			b.Fatal(err)
 		}
 	}
-		})
-	}
 }