Remove extra call to SES_Reserve_proto_priv

In h2_init_sess, an extra call was always made to SES_Reseve_proto_priv(),
even though it was already reserved. This wasted a pointer worth of
session workspace. This patch removes the extra call.

bin/varnishd/http2/cache_http2_session.c

@@ -132,7 +132,6 @@ h2_init_sess(const struct worker *wrk, struct sess *sp,
 		AZ(VHT_Init(h2->dectbl,
 			h2->local_settings.header_table_size));
 
-		XXXAN(SES_Reserve_proto_priv(sp, &up));
 		*up = (uintptr_t)h2;
 	}
 	AN(up);