Remove unused flag ami-users

Following https://github.com/scylladb/scylla-pkg/pull/4002 the ami-users
flag is no longer in use

packer/build_image.sh

@@ -28,7 +28,6 @@ print_usage() {
     echo "  [--scylla-build-sha-id] Scylla build SHA id form metadata file"
     echo "  [--branch]              Set the release branch for GCE label. Default: master"
     echo "  [--ami-regions]         Set regions to copy the AMI when done building it (including permissions and tags)"
-    echo "  [--ami-users]           A list of account IDs that have access to launch the AMI"
     echo "  [--build-tag]           Jenkins Build tag"
     echo "  --download-no-server    Download all deb needed excluding scylla from repo-for-install"
     echo "  [--build-mode]          Choose which build mode to use for Scylla installation. Default: release. Valid options: release|debug"
@@ -94,11 +93,6 @@ while [ $# -gt 0 ]; do
             echo "--ami-regions parameter: AMI_REGIONS |$AMI_REGIONS|"
             shift 2
             ;;
-        "--ami-users"):
-            AMI_USERS=$2
-            echo "--ami-users parameter: AMI_USERS |$AMI_USERS|"
-            shift 2
-            ;;
         "--log-file")
             PACKER_LOG_PATH=$2
             echo "--log-file parameter: PACKER_LOG_PATH |$PACKER_LOG_PATH|"