remove staunton submodule because it's 426Mb, copy used images

.gitmodules

@@ -4,9 +4,6 @@
 [submodule "public/vendor/tagmanager"]
 	path = public/vendor/tagmanager
 	url = https://github.com/max-favilli/tagmanager
-[submodule "public/staunton"]
-	path = public/staunton
-	url = https://github.com/clarkerubber/Staunton-Pieces
 [submodule "submodules/pdfexporter"]
 	path = submodules/pdfexporter
 	url = https://github.com/ornicar/lichessPDFExporter

conf/base.conf

@@ -9,7 +9,7 @@ net {
   ip = "5.196.91.160"
   asset {
     domain = ${net.domain}
-    version = 882
+    version = 883
   }
 }
 forcedev = false