Depreciate and remove dokku backup plugin, replace with documentation

plugins/config/backup-export

@@ -1,8 +0,0 @@
-#!/usr/bin/env bash
-set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
-
-shopt -s nullglob
-VERSION="$1"
-BASE_DIR="$2"
-
-cat; for i in $BASE_DIR/*/ENV; do echo "$i"; done

plugins/config/backup-import

@@ -1,12 +0,0 @@
-#!/usr/bin/env bash
-set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
-
-shopt -s nullglob
-VERSION="$1"
-IMPORT_DIR="$2"
-TARGET_DIR="$3"
-
-cd "$IMPORT_DIR"
-for file in */ENV; do
-  cp "$file" "$TARGET_DIR/$file"
-done