Remove a bunch of unused CTS tests from continuous test build to save space.

BUG 2053298
diff --git a/tests/SignatureTest/Android.mk b/tests/SignatureTest/Android.mk
index 01d9dee..b846ff7 100644
--- a/tests/SignatureTest/Android.mk
+++ b/tests/SignatureTest/Android.mk
@@ -15,7 +15,7 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_MODULE_TAGS := tests
+LOCAL_MODULE_TAGS := optional
 
 LOCAL_SRC_FILES := $(call all-subdir-java-files)