Update drupal-composer/drupal-scaffold to 2.6.1 to avoid redirects

Problem/Motivation

1. In repository https://github.com/goalgorilla/social_template, update package drupal-composer/drupal-scaffold to 2.6.1 -- the latest to avoid redirects while downloading the scaffold files.

See the release note of drupal-composer/drupal-scaffold https://github.com/drupal-composer/drupal-scaffold/releases/tag/2.6.1

Replace cgit.drupalcode.org with git.drupalcode.org (#104)

Following is the partial output of running composer install -vvv

> post-install-cmd: DrupalComposer\DrupalScaffold\Plugin::scaffold
  - .csslintrc (https://cgit.drupalcode.org/drupal/plain/.csslintrc?h=8.7.2): Downloading https://cgit.drupalcode.org/drupal/plain/.csslintrc?h=8.7.2
Downloading (connecting...)
Following redirect (2) https://cgit.drupalcode.org/project/drupal/raw/8.7.2/.csslintrc
Downloading https://cgit.drupalcode.org/project/drupal/raw/8.7.2/.csslintrc

Following redirect (3) https://git.drupalcode.org/project/drupal/raw/8.7.2/.csslintrc
Downloading https://git.drupalcode.org/project/drupal/raw/8.7.2/.csslintrc
Downloading (100%)
  - .editorconfig (https://cgit.drupalcode.org/drupal/plain/.editorconfig?h=8.7.2): Downloading https://cgit.drupalcode.org/drupal/plain/.editorconfig?h=8.7.2
Downloading (connecting...)
Following redirect (2) https://cgit.drupalcode.org/project/drupal/raw/8.7.2/.editorconfig
Downloading https://cgit.drupalcode.org/project/drupal/raw/8.7.2/.editorconfig

2. Does it necessary to download scaffold files, every time?

See https://github.com/drupal-composer/drupal-scaffold#usage

Once drupal-scaffold is required by your project, it will automatically update your scaffold files whenever composer update changes the version of drupal/core installed.

Proposed resolution

1. Update drupal-composer/drupal-scaffold to 2.6.1
2. Get rid of code below in composer.json

    "scripts": {
      "post-install-cmd": [
        "DrupalComposer\\DrupalScaffold\\Plugin::scaffold"
      ],
      "post-update-cmd": [
        "DrupalComposer\\DrupalScaffold\\Plugin::scaffold"
      ]
    },

Remaining tasks

- Needs discussion or confirmation
- PR(s)