chore: remove Drone pipeline and Dockerfile

Gitea Actions replaced Drone, and the Dockerfile packaged a Java 11 image
of a jar that runs on the Pi, not in Docker. The backend image comes with
the backend itself.

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

.drone.yml

@@ -1,18 +0,0 @@
-kind: pipeline
-type: docker
-name: default
-
-steps:
-- name: test
-  image: maven:3-jdk-11
-  commands:
-  - mvn install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
-  - mvn test -B
-- name: docker
-  image: plugins/docker
-  settings:
-    repo: registry.mariuszpacek.pl/home-pump
-    tags: latest
-  when:
-    branch:
-      - master

Dockerfile

@@ -1,4 +0,0 @@
-FROM amazoncorretto:11.0.17
-COPY target/test*.jar app/home-pump.jar
-
-CMD ["java", "-jar", "app/home-pump.jar"]