Remove extern/editing_typedefs.js

This file seems to have been replaced by node_extern.js.

By removing this, `java -jar /path/to/compiler.jar --language_in=ECMASCRIPT6 --language_out=ECMASCRIPT3 --js *.js commands/*.js externs/*.js testing/*.js` can be passed. However, we need to fix the files more in order to pass the tests with the type checking `--jscomp_error=checkTypes`