build: agent is the image's default entrypoint; drop the old server examples (#7)

Dockerfile

@@ -8,7 +8,7 @@ COPY . .
 ARG VERSION=dev
 ARG COMMIT=unknown
 ARG BUILD_TIME=unknown
-RUN for cmd in server:package-updater master:updater-master agent:updater-agent; do \
+RUN for cmd in master:updater-master agent:updater-agent; do \
       CGO_ENABLED=0 go build \
         -ldflags="-s -w \
           -X main.version=${VERSION} \
@@ -20,5 +20,5 @@ RUN for cmd in server:package-updater master:updater-master agent:updater-agent;
 FROM alpine:3.20
 RUN apk add --no-cache docker-cli docker-cli-compose ca-certificates wget
 COPY --from=build /out/ /usr/local/bin/
-EXPOSE 8080
-ENTRYPOINT ["/usr/local/bin/package-updater"]
+EXPOSE 8080 8090
+ENTRYPOINT ["/usr/local/bin/updater-agent"]