Stop including `.exe` files in releases

[lmatayoshi]

Since the very beginning Collectors are jusing just the .msi installer. Let's remove the .exe and related files from the build & releases, so nobody uses them and thus making things simpler

[lmatayoshi]

@mmuller from version 1.1.2 on, whenever you go to https://github.com/instedd/maap-collector/releases to download the Collector for any of the instances, you shouldn't see the .exe related files for Windows anymore compared with previous versions