MDL-80173 reportbuilder: remove various Oracle support/workarounds.

"True happiness is to rejoice in the
        <removal of Oracle compatibility>."

Reference: ba1f9cb2, 892b68d5, c63af985, 208adcf3, 9a244403, 3894fa94,
62d22c66, 628541b5, 429508a7.

admin/classes/reportbuilder/local/entities/task_log.php

@@ -271,8 +271,6 @@ class task_log extends base {
      * @return filter[]
      */
     protected function get_all_filters(): array {
-        global $DB;
-
         $tablealias = $this->get_table_alias('task_log');
 
         // Name filter (Filter by classname).
@@ -330,7 +328,7 @@ class task_log extends base {
             'output',
             new lang_string('task_logoutput', 'admin'),
             $this->get_entity_name(),
-            $DB->sql_cast_to_char("{$tablealias}.output")
+            "{$tablealias}.output"
         ))
             ->add_joins($this->get_joins());