[8.x](backport #5868) remove DEV=true from CI build steps (#5870)

* Fix like elastic/beats#41270 (#5868)

(cherry picked from commit c9cd580)

# Conflicts:
#	.buildkite/scripts/steps/integration-package.sh
#	.buildkite/scripts/steps/k8s-extended-tests.sh

* Update integration-package.sh

* Update k8s-extended-tests.sh

---------

Co-authored-by: Lee E Hinman <57081003+leehinman@users.noreply.github.com>
Co-authored-by: Pierre HILBERT <pierre.hilbert@elastic.co>

.buildkite/scripts/steps/integration-package.sh

@@ -3,4 +3,4 @@ set -euo pipefail
 
 source .buildkite/scripts/common.sh
 
-PACKAGES=tar.gz,zip,rpm,deb PLATFORMS=linux/amd64,linux/arm64,windows/amd64  SNAPSHOT=true EXTERNAL=true  DEV=true mage package
+PACKAGES=tar.gz,zip,rpm,deb PLATFORMS=linux/amd64,linux/arm64,windows/amd64  SNAPSHOT=true EXTERNAL=true  mage package

.buildkite/scripts/steps/k8s-extended-tests.sh

@@ -25,7 +25,7 @@ else
   exit 10
 fi
 
-DEV=true SNAPSHOT=true EXTERNAL=true PACKAGES=docker mage -v package
+SNAPSHOT=true EXTERNAL=true PACKAGES=docker mage -v package
 TEST_INTEG_CLEAN_ON_EXIT=true INSTANCE_PROVISIONER=kind STACK_PROVISIONER=stateful SNAPSHOT=true mage integration:kubernetesMatrix
 TESTS_EXIT_STATUS=$?
 set -e