Remove drupal/file_mdm dependency

Problem/Motivation

#3010020: Update image_effects 1.0 to 2.2 updated the image_effects module and introduced a specific version requirement for drupal/file_mdm. The drupal/file_mdm module is now a few versions up and the version we require uses the lsolesen/pel library which causes a lot of warnings on PHP 7.4

Deprecated function: Array and string offset access syntax with curly braces is deprecated in include() (line 478 of /var/www/vendor/composer/ClassLoader.php)

#0 /var/www/html/core/includes/bootstrap.inc(600): _drupal_error_handler_real(8192, 'Array and strin...', '/var/www/vendor...', 410, Array)
#1 /var/www/vendor/composer/ClassLoader.php(478): _drupal_error_handler(8192, 'Array and strin...', '/var/www/vendor...', 410, Array)
#2 /var/www/vendor/composer/ClassLoader.php(478): include()
#3 /var/www/vendor/composer/ClassLoader.php(346): Composer\Autoload\includeFile('/var/www/vendor...')
#4 [internal function]: Composer\Autoload\ClassLoader->loadClass('lsolesen\\pel\\Pe...')
#5 /var/www/vendor/lsolesen/pel/src/PelDataWindow.php(96): spl_autoload_call('lsolesen\\pel\\Pe...')
#6 /var/www/vendor/lsolesen/pel/src/PelJpeg.php(286): lsolesen\pel\PelDataWindow->__construct('\xFF\xD8\xFF\xE0\x00\x10JFIF\x00\x01\x01\x00\x00...')
#7 /var/www/vendor/lsolesen/pel/src/PelJpeg.php(123): lsolesen\pel\PelJpeg->loadFile('public://04.jpg')
#8 /var/www/html/modules/contrib/file_mdm/file_mdm_exif/src/Plugin/FileMetadata/Exif.php(108): lsolesen\pel\PelJpeg->__construct('public://04.jpg')

We added the module as per #2856573: Integration with File Metadata Manager module mentioned in https://github.com/goalgorilla/open_social/pull/1069#issuecomment-450328821

An additional issue is that image effects requires file_mdm 2 but doesn't actually get it (this requirement can be seen in image_effects/composer.json)

        "drupal/file_mdm_exif": "^2",
        "drupal/file_mdm_font": "^2"

Steps to reproduce

Proposed resolution

Remove our dependency on drupal/file_mdm as we don't actually use the module directly. The correct version will be installed by the image_effects module.

Remaining tasks

User interface changes

API changes

Data model changes