Refactor if.

* Terminate on ValueError `else` proceed.
Execute removeContact inside try.

* It may raise ValueError if contact is absent.
No need to double-check.

* Contact class overloads equality; removing a contact is
  as straightforward as removing a contactID. Check the
  unit tests for kbucket::removeContact.
Merge pull request #1 from Renelvon/SearchTime

Fix OptimizedRoutingTable::removeContact to catch ValueErrors.