refactor: make GetRand a template, remove GetRandInt

src/blockencodings.cpp

@@ -17,7 +17,7 @@
 #include <unordered_map>
 
 CBlockHeaderAndShortTxIDs::CBlockHeaderAndShortTxIDs(const CBlock& block, bool fUseWTXID) :
-        nonce(GetRand(std::numeric_limits<uint64_t>::max())),
+        nonce(GetRand<uint64_t>()),
         shorttxids(block.vtx.size() - 1), prefilledtxn(1), header(block) {
     FillShortTxIDSelector();
     //TODO: Use our mempool prior to block acceptance to predictively fill more than just the coinbase