fix(event-subscriber-example): remove event.go

the file was removed from zoraxy_plugin, but since `build_all.sh` works
by copying the module to the plugins this change wasn't propagated. This
fix removed the leftover file and updates `build_all.sh` to delete the
existing `zoraxy_plugin` module of the plugins before copying over the
updated code.

example/plugins/build_all.sh

@@ -4,6 +4,11 @@
 echo "Copying zoraxy_plugin to all mods"
 for dir in ./*; do
     if [ -d "$dir" ]; then
+        # remove existing zoraxy_plugin module, if it exists
+        if [ -d "${dir}/mod/zoraxy_plugin" ]; then
+            rm -r $dir/mod/zoraxy_plugin
+        fi
+        # copy over updated module
         cp -r ../../src/mod/plugins/zoraxy_plugin "$dir/mod"
     fi
 done