Remove dependency on facets version 1.x

Note that this is tricky to test using composer install - the patch attached won't apply as it's missing the following lines:

 # Information added by Drupal.org packaging script on 2021-01-07
 version: '1.0.0'

and using cweagans/composer-patches helper tries to update dependencies before adding patches, so composer gives up before recognizing the changed requirements:

$ composer install
Gathering patches from patch file.
Installing dependencies from lock file (including require-dev)
Verifying lock file contents can be installed on current platform.
Package operations: 1 install, 0 updates, 0 removals
Gathering patches from patch file.
Gathering patches for dependencies. This might take a minute.
  - Installing drupal/select_a11y (1.0.0): Extracting archive
  - Applying patches for drupal/select_a11y
    PATCHES/facets-requirement.patch (Remove dependency version - https://www.drupal.org/project/select_a11y/issues/3274075)

Generating autoload files

$ composer require drupal/facets:^2.0.2
./composer.json has been updated
Running composer update drupal/facets
Gathering patches from patch file.
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - drupal/select_a11y is locked to version 1.0.0 and an update of this package was not requested.
    - drupal/select_a11y 1.0.0 requires drupal/facets ^1.5 -> found drupal/facets[dev-1.x, 1.5.0, ..., 1.x-dev (alias of dev-1.x)] but it conflicts with your root composer.json require (^2.0.2).

Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.

Installation failed, reverting ./composer.json and ./composer.lock to their original content.