Don't force color diagnostics.

Clang does this automatically for you now, and forcing it causes ugly
(and difficult to parse) error diagnostics for non-color terminals.

Change-Id: I5ceb673ad50ad99cb78c733d18ac7dbfe8f978d3
diff --git a/build/Android.common_build.mk b/build/Android.common_build.mk
index b3d1380..5dd9f15 100644
--- a/build/Android.common_build.mk
+++ b/build/Android.common_build.mk
@@ -144,11 +144,8 @@
 ART_TARGET_CLANG_CFLAGS_arm64 += \
   -fno-vectorize
 
-# Colorize clang compiler warnings.
-art_clang_cflags := -fcolor-diagnostics
-
 # Warn about thread safety violations with clang.
-art_clang_cflags += -Wthread-safety
+art_clang_cflags := -Wthread-safety
 
 # Warn if switch fallthroughs aren't annotated.
 art_clang_cflags += -Wimplicit-fallthrough