remove unused GHCJS Git submodule

Author: peterbecich

.gitmodules

@@ -1,7 +1,3 @@
 [submodule "third_party/blockly"]
   path = third_party/blockly
   url = https://github.com/stefan-j/blockly
-[submodule "ghcjs"]
-  path = ghcjs
-  url = https://github.com/ghcjs/ghcjs.git
-  branch = 8.6