Move CallStack to libbacktrace.

Fix a small bug in the Printer for strings that didn't properly
prepend the prefix.

Change-Id: I33c63841ef6e07728ab3195886539d82b38ee19a
diff --git a/include/utils/ProcessCallStack.h b/include/utils/ProcessCallStack.h
index 4a86869..32458b8 100644
--- a/include/utils/ProcessCallStack.h
+++ b/include/utils/ProcessCallStack.h
@@ -39,7 +39,7 @@
     ~ProcessCallStack();
 
     // Immediately collect the stack traces for all threads.
-    void update(int32_t maxDepth = CallStack::MAX_DEPTH);
+    void update();
 
     // Print all stack traces to the log using the supplied logtag.
     void log(const char* logtag, android_LogPriority priority = ANDROID_LOG_DEBUG,