Makefile: remove mode-check target (#12505)

The Makefile would check for executable files inside the Packer
repository, and produce errors if one was detected and not explicitely
whitelisted through the `EXECUTABLE_FILES' Makefile variable.

This check was introduced a while back to avoid having executable files
in the repository, but this check can be problematic sometimes because
of how it is written, namely when building the website, which causes a
lot of JS executable files to appear in the hierarchy, and in turn this
causes the shell expansion to fail because of the large number of
arguments.

Since this test is not necessary for Packer to build or test, and since
it implies that we have to maintain the whitelist regex, we remove it
from the Makefile.

Makefile

@@ -12,8 +12,6 @@ GOOS=$(shell go env GOOS)
 GOARCH=$(shell go env GOARCH)
 GOPATH=$(shell go env GOPATH)
 
-EXECUTABLE_FILES=$(shell find . -type f -executable | egrep -v '^\./(website/[vendor|tmp]|vendor/|\.git|bin/|scripts/|pkg/)' | egrep -v '.*(\.sh|\.bats|\.git)' | egrep -v './provisioner/(ansible|inspec)/test-fixtures/exit1')
-
 # Get the git commit
 GIT_DIRTY=$(shell test -n "`git status --porcelain`" && echo "+CHANGES" || true)
 GIT_COMMIT=$(shell git rev-parse --short HEAD)
@@ -133,15 +131,6 @@ fmt-check: fmt ## Check go code formatting
 		exit 1; \
 	fi
 
-mode-check: ## Check that only certain files are executable
-	@echo "==> Checking that only certain files are executable..."
-	@if [ ! -z "$(EXECUTABLE_FILES)" ]; then \
-		echo "These files should not be executable or they must be white listed in the Makefile:"; \
-		echo "$(EXECUTABLE_FILES)" | xargs -n1; \
-		exit 1; \
-	else \
-		echo "Check passed."; \
-	fi
 fmt-docs:
 	@find ./website/pages/docs -name "*.md" -exec pandoc --wrap auto --columns 79 --atx-headers -s -f "markdown_github+yaml_metadata_block" -t "markdown_github+yaml_metadata_block" {} -o {} \;
 
@@ -166,7 +155,7 @@ generate-check: generate ## Check go code generation is on par
 		exit 1; \
 	fi
 
-test: mode-check vet ## Run unit tests
+test: vet ## Run unit tests
 	@go test -count $(COUNT) $(TEST) $(TESTARGS) -timeout=3m
 
 # acctest runs provisioners acceptance tests
@@ -178,7 +167,7 @@ testacc: # install-build-deps generate ## Run acceptance tests
 	@echo "WARN: Acceptance tests will take a long time to run and may cost money. Ctrl-C if you want to cancel."
 	PACKER_ACC=1 go test -count $(COUNT) -v $(TEST) $(TESTARGS) -timeout=120m
 
-testrace: mode-check vet ## Test with race detection enabled
+testrace: vet ## Test with race detection enabled
 	@go test -count $(COUNT) -race $(TEST) $(TESTARGS) -timeout=3m -p=8
 
 # Runs code coverage and open a html page with report