Remove deprecated code from HTML.php and FormattableMarkup.php

pradhumanjain2311 → made their first commit to this issue’s fork.

This failed on the following so sent for a retest.

Drupal\Tests\migrate\Unit\MigrationTest::testMigrationDependenciesInConstructor
    with data set "invalid key" (array(array()))
    This test did not perform any assertions

That said the code removed says it should be replaced with a PHP error fired?

This overlaps with another, will see if it's needed.

MR can be closed these overlapped with other tickets.