Remove unused test variables from Makefile

Makefile

@@ -1,5 +1,4 @@
 SRC_DIR    := ./src
-TEST_DIR   := ./script
 VENDOR_DIR := ./vendor
 
 SRC_FILES := \
@@ -32,9 +31,6 @@ TEST_PREREQS := \
 	$(SHUNIT2) \
 	$(STUB_SH)
 
-TEST_FILES := \
-	$(TEST_DIR)/**/*.zsh
-
 all: $(ALL_TARGETS)
 
 $(PLUGIN_TARGET): $(HEADER_FILES) $(SRC_FILES)