docs: Revert "update proxy section with correct env vars"

This reverts commit 1c9bbee3

Those env vars already get set by the startup script given PROXY

examples/docker-compose-proxied.yml

@@ -0,0 +1,16 @@
+version: '3'
+
+services:
+  mc:
+#    build: .
+    image: itzg/minecraft-server
+    ports:
+      - 25565:25565
+    environment:
+      EULA: "TRUE"
+#      TYPE: SPIGOT
+#      VERSION: 1.11.2
+      PROXY: proxy:3128
+  proxy:
+    image: sameersbn/squid
+