Remove call to SES_Reserve_proto_priv in h2_init_sess

h2_init_sess can only be reached through H1 with either previous knowledge
or opportunistic upgrade. Because of this the proto_priv session attribute
will always be set before entry. This patch simplifies and removes dead
code containing a call to SES_Reserve_proto_priv.

Note: Better diff with the --ignore-all-space option

bin/varnishd/http2/cache_http2_session.c

@@ -101,12 +101,11 @@ h2_init_sess(const struct worker *wrk, struct sess *sp,
 	uintptr_t *up;
 	struct h2_sess *h2;
 
-	if (SES_Get_proto_priv(sp, &up)) {
-		/* Already reserved if we came via H1 */
-		XXXAN(SES_Reserve_proto_priv(sp, &up));
-		*up = 0;
-	}
-	if (*up == 0) {
+	/* proto_priv session attribute will always have been set up by H1
+	 * before reaching here. */
+	AZ(SES_Get_proto_priv(sp, &up));
+	assert(*up == 0);
+
 	if (srq == NULL)
 		srq = Req_New(wrk, sp);
 	AN(srq);
@@ -129,13 +128,10 @@ h2_init_sess(const struct worker *wrk, struct sess *sp,
 	h2->remote_settings = H2_proto_settings;
 	h2->decode = decode;
 
-		AZ(VHT_Init(h2->dectbl,
-			h2->local_settings.header_table_size));
+	AZ(VHT_Init(h2->dectbl, h2->local_settings.header_table_size));
 
 	*up = (uintptr_t)h2;
-	}
-	AN(up);
-	CAST_OBJ_NOTNULL(h2, (void*)(*up), H2_SESS_MAGIC);
+
 	return (h2);
 }