Following from this webpage https://msdn.microsoft.com/en-us/library/ms228998.aspx
which states:
you can disable this option by clearing the Use ".deploy" file extension option on the Publish Options Dialog Box,
Where is the "Use .deploy file extension" option in VS 2017? It's not in the Publish Options Dialog Box anymore. HELP
Right click the project. Choose Properties. From there switch to the Publish tab, click Options... and switch to the Deployment tab.