MDL-37600 qtype match: remove obsolete DB columns, and obey coding style.

Tables renamed to start qtype_match, and qtype_match_options.subquestions
and qtype_match_subquestions.code columnd dropped. Also, qtype_match_options
-> question foreign key link changed to be foreign-unique, since that is
what it should be.
MDL-37600 qtype match: fix codechecker issues.
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