Remove libunwind-ptrace dependency.

Change-Id: Iae4a73546f672c208ffe1b224e8d9a9e693f95f0
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index b875efd..54cace9 100644
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -57,7 +57,6 @@
 libbacktrace_shared_libraries := \
 	libbase \
 	libunwind \
-	libunwind-ptrace \
 
 libbacktrace_shared_libraries_host := \
 	liblog \