Revert "MINOR: chunks: Make sure trash_size is only set once."

This reverts commit 1c3b83242da96f1d94ef3df34c399c1b984668b6.

It was made only to silence the thread sanitizer but ends up creating a
bug. Indeed, if "tune.bufsize" is in the global section, the trash_size
value is not updated anymore and the trash becomes smaller than a buffer!

Let's stop trying to fix the thread sanitizer reports, they are invalid,
and trying to fix them actually introduces bugs where there were none.

See GH issue #117 for more context. No backport is needed.
diff --git a/src/chunk.c b/src/chunk.c
index 344b28d..8e77858 100644
--- a/src/chunk.c
+++ b/src/chunk.c
@@ -68,9 +68,8 @@
  */
 static int alloc_trash_buffers(int bufsize)
 {
-	int old = 0;
 	chunk_init(&trash, my_realloc2(trash.area, bufsize), bufsize);
-	HA_ATOMIC_CAS(&trash_size, &old, bufsize);
+	trash_size = bufsize;
 	trash_buf1 = (char *)my_realloc2(trash_buf1, bufsize);
 	trash_buf2 = (char *)my_realloc2(trash_buf2, bufsize);
 	return trash.area && trash_buf1 && trash_buf2;