Provide ways to delete obsolete results

When a test is performed, probably only newest results matter and older ones are obsolete. So it should be possible to delete them automatically or manually.

A test is obsolete when it is related to test X, but test X is also related to a newer TR.

AUTO
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Config option: 'autoclean'
Possible values:
* 0 - no
* 1- yes, everytime deinit_status() is called, it should delete older versions of current test
* 2 - everytime deinit_status() is called, it should delete ALL obsolete results

MANUAL
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* VOID results_clean(tr_type, tr_name)
  * tr_type: 'tc' or 'ts'
  * tr_name: name of tc/ts
* VOID all_results_clean()