Stop manually including gtest headers.

libgtest exports these.

Test: mm
Bug: http://b/16574165
Change-Id: I4f6220c6d3fe67f4a21451d2f7e790705519d935
diff --git a/build/Android.gtest.mk b/build/Android.gtest.mk
index c09241a..0340e10 100644
--- a/build/Android.gtest.mk
+++ b/build/Android.gtest.mk
@@ -634,6 +634,7 @@
   LOCAL_SRC_FILES := $$(art_gtest_filename)
   LOCAL_C_INCLUDES += $$(ART_C_INCLUDES) art/runtime art/cmdline $$(art_gtest_extra_c_includes)
   LOCAL_SHARED_LIBRARIES += libartd $$(art_gtest_extra_shared_libraries) libart-gtest libartd-disassembler
+  LOCAL_STATIC_LIBRARIES += libgtest
   LOCAL_WHOLE_STATIC_LIBRARIES += libsigchain
 
   LOCAL_ADDITIONAL_DEPENDENCIES := art/build/Android.common_build.mk