txscript: Optimize ExtractPkScriptAddrs pubkey.
txscript: Optimize ExtractPkScriptAddrs pubkey.

This continues the process of converting the ExtractPkScriptAddrs
function to use the optimized extraction functions recently introduced
as part of the typeOfScript conversion.

In particular, this converts the detection for pay-to-pubkey scripts.

tb00/btcd,davecgh/btcd,btcsuite/btcd,davecgh/btcd,ltcsuite/ltcd,tb00/btcd,btcsuite/btcd,ltcsuite/ltcd