Replace EF tests submodule with a makefile

Makefile

@@ -0,0 +1,31 @@
+TESTS_TAG := v0.8.3
+TESTS = general minimal mainnet
+
+TESTS_BASE_DIR := ./tests/ef_tests
+REPO_NAME := eth2.0-spec-tests
+OUTPUT_DIR := $(TESTS_BASE_DIR)/$(REPO_NAME)
+
+BASE_URL := https://github.com/ethereum/$(REPO_NAME)/releases/download/$(SPEC_VERSION)
+
+release:
+	cargo build --all --release
+
+clean_ef_tests:
+	rm -r $(OUTPUT_DIR)
+
+ef_tests: download_tests extract_tests
+	mkdir $(OUTPUT_DIR)
+	for test in $(TESTS); do \
+		tar -C $(OUTPUT_DIR) -xvf $(TESTS_BASE_DIR)/$$test.tar ;\
+		rm $(TESTS_BASE_DIR)/$$test.tar ;\
+	done
+
+extract_tests:
+	for test in $(TESTS); do \
+		gzip -df $(TESTS_BASE_DIR)/$$test.tar.gz ;\
+	done
+
+download_tests:
+	for test in $(TESTS); do \
+		wget -P $(TESTS_BASE_DIR) $(BASE_URL)/$$test.tar.gz; \
+	done