There are two warnings on blocks/spam_deletion/viewvotes.php in Moodle 2.8. I am unsure about earlier versions.

You need to update your sql to include additional name fields in the user object.
line 3581 of /lib/moodlelib.php: call to debugging()
line 517 of /blocks/spam_deletion/lib.php: call to fullname()
line 761 of /lib/tablelib.php: call to spam_report_table->col_spammer()
line 1385 of /lib/tablelib.php: call to flexible_table->format_row()
line 1497 of /lib/tablelib.php: call to table_sql->build_table()
line 36 of /blocks/spam_deletion/viewvotes.php: call to table_sql->out()
You need to update your sql to include additional name fields in the user object.
line 3581 of /lib/moodlelib.php: call to debugging()
line 563 of /blocks/spam_deletion/lib.php: call to fullname()
line 761 of /lib/tablelib.php: call to forum_spam_report_table->col_votecount()
line 1385 of /lib/tablelib.php: call to flexible_table->format_row()
line 1497 of /lib/tablelib.php: call to table_sql->build_table()
line 36 of /blocks/spam_deletion/viewvotes.php: call to table_sql->out()

Apparently the following is displayed after deleting a spammer.

get_system_context() is deprecated, please use context_system::instance() instead.

line 3714 of /lib/deprecatedlib.php: call to debugging()
line 37 of /blocks/spam_deletion/confirmdelete.php: call to get_system_context()

session_kill_user() is deprecated, use \core\session\manager::kill_user_sessions() instead

line 197 of /lib/deprecatedlib.php: call to debugging()
line 142 of /blocks/spam_deletion/lib.php: call to session_kill_user()
line 246 of /blocks/spam_deletion/lib.php: call to spammerlib->set_profile_as_spammer()
line 56 of /blocks/spam_deletion/confirmdelete.php: call to spammerlib->set_spammer()

add_to_log() has been deprecated, please rewrite your code to the new events API

line 48 of /lib/deprecatedlib.php: call to debugging()
line 58 of /blocks/spam_deletion/confirmdelete.php: call to add_to_log()