libutilscallstack: removed from darwin

libbacktrace only includes its Backtrace.cpp on the linux targets
but not windows or darwin targets. So, both should be disabled.

Previously, libutilscallstack was only ever a static library on
these platforms. Since nothing provided the symbols, these targets
couldn't have been used.

Fixes: 129636352
Test: m

Change-Id: I3f0b09e1d67c485b3ea57f58d1220d9516b326f2

libutils/Android.bp

@@ -183,6 +183,9 @@ cc_library {
                 "ProcessCallStack.cpp",
             ],
         },
+        darwin: {
+            enabled: false,
+        },
         windows: {
             enabled: false,
         },