remove unused code #4183

The title is self-explanatory, Obviously, you might want to keep some of those, so I'm waiting for feedback.

Did some digging using git's pickaxe...

ACK on removing:

• CWallet::AddReserveKey : Was never used at all, added by @sipa back in 2011 in 30ab2c9c
• CTransaction::IsNewerThan: Was used by the transaction replacement code which was removed in 98c7c8fd
• LogException: Hasn't been used for as long as Satoshi was still here
• LookupHostNumeric: Is simply a wrapper for LookupHost(_1, _2, _3, false), no need for this we can pass a boolean if we need this functionality.
• CBlockIndex::GetMedianTime: was used in CWalletTx::GetTxTime until 471426fb3, in 2011

NACK on removing:

• CWallet::GetDestData: part of the *DestData API, which is planned to be used more extensively by the GUI
• CNetAddr::IsMulticast: part of basic 'what is this address' functionality - though it's doubtful we will use multicast, we might want to detect these addresses for error robustness or such.
• CDBEnv::RemoveDb: doubtful that we'll ever allow removing wallets - but for API symmetry it makes sense to keep this function
• CService::SetPort: API symmetry, run-time configurability
• UnregisterWallet: it's probably a bug that this isn't used - and will certainly be needed if someone ever implements multi-wallet support

Not sure:

• CPubKey::VerifyCompact: counterpart to CKey::SignCompact which is used, but seems that we use RecoverCompact instead in verifymessage()

Dropped the removal of functions under "NACK on removing" and "Not sure". Rebased against master.

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