test: Remove UNITTEST params

UNITTEST parameter are not used by any current tests, and the model
(modifyable parameters) is inconvenient when unit-testing. As
they are stored in a global structure eevery test
would have to (re)set up its own parameters.

For consistency it is also better to test with MAIN parameters.

src/chainparamsbase.cpp

@@ -82,9 +82,6 @@ void SelectBaseParams(CBaseChainParams::Network network)
     case CBaseChainParams::REGTEST:
         pCurrentBaseParams = &regTestParams;
         break;
-    case CBaseChainParams::UNITTEST:
-        pCurrentBaseParams = &unitTestParams;
-        break;
     default:
         assert(false && "Unimplemented network");
         return;