feat: update Suspense usage (#2099)

See https://github.com/vuejs/vue-next/pull/2099 for details.

packages/server-renderer/src/helpers/ssrRenderSuspense.ts

@@ -5,9 +5,7 @@ export async function ssrRenderSuspense(
   { default: renderContent }: Record<string, (() => void) | undefined>
 ) {
   if (renderContent) {
-    push(`<!--[-->`)
     renderContent()
-    push(`<!--]-->`)
   } else {
     push(`<!---->`)
   }

packages/server-renderer/src/render.ts

@@ -33,8 +33,7 @@ const {
   setCurrentRenderingInstance,
   setupComponent,
   renderComponentRoot,
-  normalizeVNode,
-  normalizeSuspenseChildren
+  normalizeVNode
 } = ssrUtils
 
 export type SSRBuffer = SSRBufferItem[] & { hasAsync?: boolean }
@@ -200,11 +199,7 @@ export function renderVNode(
       } else if (shapeFlag & ShapeFlags.TELEPORT) {
         renderTeleportVNode(push, vnode, parentComponent)
       } else if (shapeFlag & ShapeFlags.SUSPENSE) {
-        renderVNode(
-          push,
-          normalizeSuspenseChildren(vnode).content,
-          parentComponent
-        )
+        renderVNode(push, vnode.ssContent!, parentComponent)
       } else {
         warn(
           '[@vue/server-renderer] Invalid VNode type:',