Remove unnecessary flags in NDK build.

Change-Id: Ib5b4d0b7f2d898671252734978c789b8171d96a8

jni/Android.mk

diff --git a/jni/Android.mk b/jni/Android.mk
index ef31946..5495176 100644
--- a/jni/Android.mk
+++ b/jni/Android.mk
@@ -81,7 +81,6 @@
 LOCAL_C_INCLUDES += $(EIGEN_PATH)
 
 LOCAL_CPP_EXTENSION := .cc
-LOCAL_CPPFLAGS += -O3
 LOCAL_CFLAGS := $(CERES_EXTRA_DEFINES) \
                 -DCERES_DONT_HAVE_PROTOCOL_BUFFERS \
                 -DCERES_NO_SUITESPARSE \