Makefile: directly call scripts instead of using variables

These variables serve no purpose as they are only used once. Drop them,
and call the scripts directly.

This also fixes some of the unnecessary inconsistencies like

  PREPARE_SCRIPT = hack/prepare.sh
  MAKE_E2E_FAST = hack/deploy_fast.sh

  prepare-e2e-test:
      bash $(PREPARE_SCRIPT)
  fast_e2e_test: prepare-e2e-test
      bash $(MAKE_E2E_FAST)

where the variable names, the script names and the Make targets have no
obvious resemblance (with the change, the Make targets are still
inconsistent with the underlying scripts).

Also, the scripts are executable and have a shebang. They choose their
interpreter themselves and the Makefile should not assume that this is
always "bash".

Makefile

@@ -73,35 +73,28 @@ CONTAINER_TOOL ?= podman
 SHELL = /usr/bin/env bash -o pipefail
 .SHELLFLAGS = -ec
 
-# Define the scripts with their paths in the hack folder
-PREPARE_SCRIPT = hack/prepare.sh
-IPU_HOST_SCRIPT = hack/ipu_host_deploy.sh
-IPU_DEPLOY_SCRIPT = hack/ipu_deploy.sh
-DEPLOY_TFT_SCRIPT = hack/deploy_traffic_flow_tests.sh
-MAKE_E2E_FAST = hack/deploy_fast.sh
-
 .PHONY: default
 default: build
 
 .PHONY: prepare-e2e-test
 prepare-e2e-test:
-	bash $(PREPARE_SCRIPT)
+	./hack/prepare.sh
 
 .PHONY: ipu_host
 ipu_host: prepare-e2e-test
-	bash $(IPU_HOST_SCRIPT)
+	./hack/ipu_host_deploy.sh
 
 .PHONY: ipu_deploy
 ipu_deploy: prepare-e2e-test
-	bash $(IPU_DEPLOY_SCRIPT)
+	./hack/ipu_deploy.sh
 
 .PHONY: deploy_tft_tests
 deploy_tft_tests:
-	bash $(DEPLOY_TFT_SCRIPT)
+	./hack/deploy_traffic_flow_tests.sh
 
 .PHONY: fast_e2e_test
 fast_e2e_test: prepare-e2e-test
-	bash $(MAKE_E2E_FAST)
+	./hack/deploy_fast.sh
 
 .PHONY: e2e_test
 e2e-test: ipu_host ipu_deploy deploy_tft_tests