Remove mimimum_version and requirements_met from MigrateSource attribute class

It is pretty clear that requirements_met is used only in the migrate_drupal module:

$ grep -ril minimum_version core/modules/mig*
core/modules/migrate/src/Attribute/MigrateSource.php
core/modules/migrate/src/Annotation/MigrateSource.php
core/modules/migrate_drupal/tests/src/Unit/source/DrupalSqlBaseTest.php
core/modules/migrate_drupal/src/Plugin/migrate/source/DrupalSqlBase.php

The situation is less clear for requirements_met:

$ grep -ril requirements_met core/modules/mig*
core/modules/migrate/tests/modules/migrate_events_test/src/Plugin/migrate/destination/DummyDestination.php
core/modules/migrate/tests/modules/migrate_missing_database_test/src/Plugin/migrate/source/MigrateMissingDatabaseSource.php
core/modules/migrate/tests/src/Kernel/SqlBaseTest.php
core/modules/migrate/src/Plugin/Derivative/MigrateEntityRevision.php
core/modules/migrate/src/Plugin/Derivative/MigrateEntityComplete.php
core/modules/migrate/src/Plugin/Derivative/MigrateEntity.php
core/modules/migrate/src/Plugin/migrate/destination/NullDestination.php
core/modules/migrate/src/Plugin/migrate/destination/DestinationBase.php
core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
core/modules/migrate/src/Attribute/MigrateDestination.php
core/modules/migrate/src/Attribute/MigrateSource.php
core/modules/migrate/src/Annotation/MigrateDestination.php
core/modules/migrate/src/Annotation/MigrateSource.php
core/modules/migrate_drupal/tests/src/Unit/source/DrupalSqlBaseTest.php
core/modules/migrate_drupal/tests/src/Kernel/d7/FieldDiscoveryTest.php
core/modules/migrate_drupal/tests/src/Kernel/d6/FieldDiscoveryTest.php
core/modules/migrate_drupal/src/Plugin/migrate/source/DrupalSqlBase.php

Many (most? all?) of those uses refer to requirements_met in the MigrateDestination annotation and attribute classes. The attribute class is already part of Drupal 11.1.0, so it is too late to remove properties from that class without first deprecating them. But I think we can remove requirements_met from the attribute class.

I think the only place in the migrate module, outside of tests, where requirements_met refers to the source plugin (not the destination plugin) is SqlBase::checkRequirements().