Call to remove deprecated code.

Line src/Plugin/Field/FieldWidget/MaterializeDateTimeWidget.php
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166 Call to deprecated function datetime_date_default_time():
in drupal:8.5.0 and is removed from drupal:9.0.0. Use
\Drupal\Component\Datetime\DateTimePlus::setDefaultDateTime() or
\Drupal\Core\Datetime\DrupalDateTime::setDefaultDateTime() instead.
167 Call to deprecated constant DATETIME_DATE_STORAGE_FORMAT: Deprecated in drupal:8.5.0 and is removed from
drupal:9.0.0. Use \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATE_STORAGE_FORMAT instead.
171 Call to deprecated constant DATETIME_DATETIME_STORAGE_FORMAT: Deprecated in drupal:8.5.0 and is removed from
drupal:9.0.0. Use \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATETIME_STORAGE_FORMAT instead.
176 Call to deprecated constant DATETIME_STORAGE_TIMEZONE: Deprecated in drupal:8.5.0 and is removed from drupal:9.0.0.
Use \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::STORAGE_TIMEZONE instead.
224 Call to deprecated function drupal_get_user_timezone():
in drupal:8.8.0 and is removed from drupal:9.0.0. Use
date_default_timezone_get() instead.
235 Call to deprecated constant DATETIME_STORAGE_TIMEZONE: Deprecated in drupal:8.5.0 and is removed from drupal:9.0.0.
Use \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::STORAGE_TIMEZONE instead.
238 Call to deprecated constant DATETIME_DATE_STORAGE_FORMAT: Deprecated in drupal:8.5.0 and is removed from
drupal:9.0.0. Use \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATE_STORAGE_FORMAT instead.
262 Call to deprecated function datetime_date_default_time():
in drupal:8.5.0 and is removed from drupal:9.0.0. Use
\Drupal\Component\Datetime\DateTimePlus::setDefaultDateTime() or
\Drupal\Core\Datetime\DrupalDateTime::setDefaultDateTime() instead.