Conditionally include the 'samplecode' rules.

Not sure goal 'samplecode' is still used by anybody these days.

Change-Id: I808a021a6e4be6a97c4b5c256b94374c1b3dae47
diff --git a/core/main.mk b/core/main.mk
index d568f8a..2399d2e 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1004,6 +1004,7 @@
 
 .PHONY: lintall
 
+ifneq (,$(filter samplecode, $(MAKECMDGOALS)))
 .PHONY: samplecode
 sample_MODULES := $(sort $(call get-tagged-modules,samples))
 sample_APKS_DEST_PATH := $(TARGET_COMMON_OUT_ROOT)/samples
@@ -1017,6 +1018,7 @@
 	@echo "Collect sample code apks: $^"
 	# remove apks that are not intended to be installed.
 	rm -f $(sample_ADDITIONAL_INSTALLED)
+endif  # samplecode in $(MAKECMDGOALS)
 
 .PHONY: findbugs
 findbugs: $(INTERNAL_FINDBUGS_HTML_TARGET) $(INTERNAL_FINDBUGS_XML_TARGET)