Stop setting GO111MODULE=on

It's the default since Go 1.16.

In theory the environment might be setting it to off, and breaking
our builds; unless something compelling comes up, I think that
hypothetical environment should be changed, nowadays.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Makefile

@@ -15,7 +15,7 @@ BUILD_TAGS_DARWIN_CROSS = containers_image_openpgp
 BUILDTAGS = btrfs_noversion libdm_no_deferred_remove
 BUILDFLAGS := -tags "$(BUILDTAGS)"
 
-PACKAGES := $(shell GO111MODULE=on go list $(BUILDFLAGS) ./...)
+PACKAGES := $(shell go list $(BUILDFLAGS) ./...)
 SOURCE_DIRS = $(shell echo $(PACKAGES) | awk 'BEGIN{FS="/"; RS=" "}{print $$4}' | uniq)
 
 PREFIX ?= ${DESTDIR}/usr
@@ -41,7 +41,7 @@ export PATH := $(PATH):${GOBIN}
 all: tools test validate .gitvalidation
 
 build:
-	GO111MODULE="on" go build $(BUILDFLAGS) ./...
+	go build $(BUILDFLAGS) ./...
 
 $(MANPAGES): %: %.md
 	$(GOMD2MAN) -in $< -out $@
@@ -78,7 +78,7 @@ clean:
 	rm -rf $(MANPAGES)
 
 test:
-	@GO111MODULE="on" go test $(BUILDFLAGS) -cover ./...
+	@go test $(BUILDFLAGS) -cover ./...
 
 fmt:
 	@gofmt -l -s -w $(SOURCE_DIRS)

hack/validate.sh

@@ -15,7 +15,7 @@ if [[ -z $(type -P gofmt) ]]; then
 fi
 
 echo "Executing go vet"
-GO111MODULE="on" go vet -tags="$BUILDTAGS" ./...
+go vet -tags="$BUILDTAGS" ./...
 
 echo "Executing gofmt"
 OUTPUT=$(gofmt -s -l . | sed -e '/^vendor/d')