Build without BuildKit

The Jenkins worker has no buildx, so DOCKER_BUILDKIT=1 fails the build.
Drop COPY --chmod and the syntax directive, and track the init script's
executable bit in git instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Dockerfile

@@ -1,4 +1,3 @@
-# syntax=docker/dockerfile:1
 FROM ubuntu:24.04
 
 ENV DEBIAN_FRONTEND=noninteractive \
@@ -11,7 +10,7 @@ RUN apt-get update \
  && apt-get purge -y --auto-remove software-properties-common gpg-agent \
  && rm -rf /var/lib/apt/lists/*
 
-COPY --chmod=755 deluge-web_init.sh /usr/local/bin/deluge-web_init.sh
+COPY deluge-web_init.sh /usr/local/bin/deluge-web_init.sh
 
 VOLUME ["/config"]
 EXPOSE 80

Jenkinsfile

@@ -13,10 +13,6 @@ pipeline {
         cron('H H H * *')
     }
 
-    environment {
-        DOCKER_BUILDKIT = '1'
-    }
-
     stages {
         stage('Build') {
             steps {