Dub project has both .sdl and .json files. Is this normal or did I do something wrong?

[WhatMeWorry]

I've been using Dub for a while but from the very beginning I 
decided to go with SDL 100% of the time, So I've got a dub.sdl 
file like:

name "01_10_camera_view_space"
description "A minimal D application."
authors "kheaser"
copyright "Copyright © 2017, kheaser"
license "proprietary"

dependency "derelict-al"      version="~>1.0.3"
dependency "derelict-assimp3" version="~>1.3.0"
dependency "derelict-fi"      version="~>2.0.3"
dependency "derelict-fmod"    version="~>2.0.4"
dependency "derelict-ft"      version="~>1.1.3"
dependency "derelict-gl3"     version="~>1.0.23"
dependency "derelict-glfw3"   version="~>3.1.3"
dependency "derelict-util"    version="~>2.0.6"
dependency "gl3n"             version="~>1.3.1"
   .............


But when I look the directory that has the dub.sdl file, I also 
see a file called dub.selections.json

{
	"fileVersion": 1,
	"versions": {
		"derelict-al": "1.0.3",
		"derelict-assimp3": "1.3.0",
		"derelict-fi": "2.0.3",
		"derelict-fmod": "2.0.4",
		"derelict-ft": "1.1.3",
		"derelict-gl3": "1.0.23",
		"derelict-glfw3": "3.1.3",
		"derelict-util": "2.0.6",
		"gl3n": "1.3.1"
	}
}


So how did this .json file get created and can I just delete it?  
I only noticed this because when I was troubleshooting the 
project, I changed the dub.sdl library versions but the 
compile/run was using the library versions in dub.selections.json.

I did switch from using DMD to LDC, if that has any bearing.