html: drop <isindex> and <command> specific handlings

This commit also adds remaining tests to follow up on golang.org/cl/205617

Change-Id: I8b155f9f605c6a0eb8745c32f5e785f5b4bc1c7e
Reviewed-on: https://go-review.googlesource.com/c/net/+/208937
Run-TryBot: Kunpei Sakai <namusyaka@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
diff --git a/html/render.go b/html/render.go
index d34564f..8bf47ed 100644
--- a/html/render.go
+++ b/html/render.go
@@ -252,20 +252,19 @@
 // Section 12.1.2, "Elements", gives this list of void elements. Void elements
 // are those that can't have any contents.
 var voidElements = map[string]bool{
-	"area":    true,
-	"base":    true,
-	"br":      true,
-	"col":     true,
-	"command": true,
-	"embed":   true,
-	"hr":      true,
-	"img":     true,
-	"input":   true,
-	"keygen":  true,
-	"link":    true,
-	"meta":    true,
-	"param":   true,
-	"source":  true,
-	"track":   true,
-	"wbr":     true,
+	"area":   true,
+	"base":   true,
+	"br":     true,
+	"col":    true,
+	"embed":  true,
+	"hr":     true,
+	"img":    true,
+	"input":  true,
+	"keygen": true,
+	"link":   true,
+	"meta":   true,
+	"param":  true,
+	"source": true,
+	"track":  true,
+	"wbr":    true,
 }