"wlconcatenatedbody0.js" gets created when you chose to concatenate your JS files. This is a choice you make as part of your build process. The configuration to do this, is enabled via build-settings.xml. Concatenation of JS files is not on by default in Desktop browser environment.
Refer to the steps and details here.
This does not cause runtime issues, but if there is a problem, troubleshooting becomes hard. If you do not wish to have concatenation on, you should modify the settings accordingly.
