adding option to remove text format description from message form through admin interface

config/install/private_message.settings.yml

 enable_email_notifications: true
 send_by_default: true
+hide_form_filter_tips: false

config/schema/private_message.schema.yml

@@ -36,6 +36,9 @@ private_message.settings:
     send_by_default:
       type: boolean
       label: 'Whether to send emails by default. Users will be able to alter this behavior in their profiles'
+    hide_form_filter_tips:
+      type: boolean
+      label: "Whether or not to hide the filter tips on the message form"
 
 private_message.mail:
   type: config_object

src/Form/ConfigForm.php

@@ -49,6 +49,13 @@ class ConfigForm extends ConfigFormBase {
       ],
     ];
 
+    $form['hide_form_filter_tips'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Hide filter tips'),
+      '#description' => $this->t('If this box is checked, the text formats description on the private message form will be removed'),
+      '#default_value' => (int) $config->get('hide_form_filter_tips'),
+    ];
+
     return parent::buildForm($form, $form_state);
   }
 
@@ -59,6 +66,7 @@ class ConfigForm extends ConfigFormBase {
     $this->config('private_message.settings')
       ->set('enable_email_notifications', (bool) $form_state->getValue('enable_email_notifications'))
       ->set('send_by_default', (bool) $form_state->getValue('send_by_default'))
+      ->set('hide_form_filter_tips', (bool) $form_state->getValue('hide_form_filter_tips'))
       ->save();
 
     parent::submitForm($form, $form_state);

src/Form/PrivateMessageForm.php

@@ -162,6 +162,10 @@ class PrivateMessageForm extends ContentEntityForm {
       $form['#validate'][] = '::validateMembers';
 	}
 
+    if($this->config->get('hide_form_filter_tips')) {
+      $form['#after_build'][] = '::afterBuild';
+    }
+
     return $form;
   }
 
@@ -227,6 +231,15 @@ class PrivateMessageForm extends ContentEntityForm {
     return $response;
   }
 
+  /**
+   * After build callback for the Private Message Form
+   */
+  public function afterBuild(array $form, FormStateInterface $form_state) {
+    $form['message']['widget'][0]['format']['#access'] = FALSE;
+
+    return $form;
+  }
+
   /**
    * {@inheritdoc}
    */