Remove an unnecessary line in the checklist in pull_request_template.md

[Ultra980]

As Daudix told me on Discord, adding the URL in presets.json isn't needed anymore.

New Preset:

Description

Palette

• [ ] None

Screenshots (optional)

Wallpaper

Checklist

Before submitting the PR, I checked:

• [ ] I've only modified one preset
• [ ] I've added the URL to my raw preset in presets.json - the whole point of this PR is to remove this line
• [ ] I've checked the format of each json files I modified
• [ ] (optional) I've added screenshots
• [ ] The preset name is following preset naming guidelines.

Publication

• [ ] I want to add my preset in the preset list.

Thanks for your submission we will review and merge it as quick as possible.