pkg/jerryscript: do not use Makefile.base

Do not include Makefile.base as 'DIRS' are not used here.
Also if 'all' target was to be used, there would be two rules creating
`$(BINDIR)/jerryscript.a`.

By default `Makefile.jerryscript` executes `libjerry` as it is the first
target.

pkg/jerryscript/Makefile.jerryscript

@@ -33,5 +33,3 @@ libjerry:
 	cp $(BUILD_DIR)/lib/libjerry-core.a $(BINDIR)/jerryscript.a
 	cp $(BUILD_DIR)/lib/libjerry-ext.a $(BINDIR)/jerryscript-ext.a
 	cp $(BUILD_DIR)/lib/libjerry-port-default-minimal.a $(BINDIR)/jerryport-minimal.a
-
-include $(RIOTBASE)/Makefile.base