Revert "Upgrade to dlmalloc 2.8.5."

This reverts commit 999089181ef60bb67e1a49f2cf6f4ec608a7caf8.
diff --git a/libc/bionic/malloc_debug_common.c b/libc/bionic/malloc_debug_common.c
index 9333de9..4105ab8 100644
--- a/libc/bionic/malloc_debug_common.c
+++ b/libc/bionic/malloc_debug_common.c
@@ -195,19 +195,9 @@
     return dlmallinfo();
 }
 
-size_t malloc_usable_size(void* mem)
-{
-    return dlmalloc_usable_size(mem);
-}
-
-void* valloc(size_t bytes)
-{
-    return dlvalloc(bytes);
-}
-
-void* pvalloc(size_t bytes)
-{
-    return dlpvalloc(bytes);
+void* valloc(size_t bytes) {
+    /* assume page size of 4096 bytes */
+    return memalign( getpagesize(), bytes );
 }
 
 /* Support for malloc debugging.