Small cleanup of duplicated test values.

A few flags were duplicates of flags already passed when using the TEST
targets.

Change-Id: I8f0d09915f5b830050fe25635a0852e8536e3aca
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index a0ff95f..a7305da 100755
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -96,11 +96,8 @@
 	-fno-builtin \
 	-O0 \
 	-g \
-	-DGTEST_HAS_STD_STRING \
-	-fstack-protector-all \
 
 backtrace_test_cflags_target := \
-	-DGTEST_OS_LINUX_ANDROID \
 	-DENABLE_PSS_TESTS \
 
 backtrace_test_src_files := \