Remove workaround '.exe extension required`

ref [source](https://github.com/dotnet/cli/blob/ac4c6702d5d345dc9c397f80290f105fedebe98b/src/dotnet/commands/dotnet-compile-fsc/Program.cs#L93-L94)

``` fsharp
//HACK fsc raise error FS0208 if target exe doesnt have extension .exe
bool hackFS0208 = targetNetCore && commonOptions.EmitEntryPoint == true;
```
