scandir: remove dead code.

This is the second or third time I've scratched my head wondering why
this destructor has no coverage. I was tempted to leave it in with a
comment saying it should never be called, but that seemed sillier than
just replacing it with an assertion.

Test: treehugger
Change-Id: I3442d9f8a391fae668e77c6888a4457ededee494
diff --git a/libc/bionic/scandir.cpp b/libc/bionic/scandir.cpp
index 6a7e368..f528286 100644
--- a/libc/bionic/scandir.cpp
+++ b/libc/bionic/scandir.cpp
@@ -16,8 +16,9 @@
 
 #include <dirent.h>
 
-#include <fcntl.h>
+#include <assert.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -32,10 +33,8 @@
   }
 
   ~ScandirResult() {
-    while (size_ > 0) {
-      free(names_[--size_]);
-    }
-    free(names_);
+    // We always call release(), so this can't happen.
+    if (names_ != nullptr) __assert(__FILE__, __LINE__, "missing call to release()");
   }
 
   size_t size() {