[skip travis] fix remove qemu (#138)

qemu doesn't apply to custom builds

Author: RaymondMouthaan

docker-custom/Dockerfile.custom

@@ -66,8 +66,7 @@ COPY --from=build /usr/src/node-red/prod_node_modules ./node_modules
 # Chown, install devtools & Clean up
 RUN chown -R node-red:node-red /usr/src/node-red && \
     /tmp/install_devtools.sh && \
-    rm /tmp/* && \
-    rm /usr/bin/qemu-$QEMU_ARCH-static
+    rm /tmp/*
 
 USER node-red