libutils: remove unused 'CALLSTACKS'

This macro is set, but it doesn't exist.

Bug: 302720583
Test: build
Change-Id: I88032c24b8bc8dc52d521e769149cbd8f619dde8
diff --git a/libutils/Android.bp b/libutils/Android.bp
index 2c05fbc..0f63df4 100644
--- a/libutils/Android.bp
+++ b/libutils/Android.bp
@@ -208,7 +208,6 @@
     defaults: ["libutils_impl_defaults"],
 
     cflags: [
-        "-DCALLSTACKS=1",
         "-DDEBUG_POLL_AND_WAKE=1",
         "-DDEBUG_REFS=1",
         "-DDEBUG_TOKENIZER=1",