refactor: inline constant return value of CDBWrapper::WriteBatch

`WriteBatch` can only ever return `true` - its errors are handled by throwing a `throw dbwrapper_error` instead.
The boolean return value is quite confusing, especially since it's symmetric with `CDBWrapper::Read`, which catches the exceptions and returns a boolean instead.
We're removing the constant return value and inlining `true` for its usages.

src/index/base.cpp

@@ -262,7 +262,7 @@ bool BaseIndex::Commit()
         ok = CustomCommit(batch);
         if (ok) {
             GetDB().WriteBestBlock(batch, GetLocator(*m_chain, m_best_block_index.load()->GetBlockHash()));
-            ok = GetDB().WriteBatch(batch);
+            GetDB().WriteBatch(batch);
         }
     }
     if (!ok) {

src/index/blockfilterindex.cpp

@@ -338,7 +338,7 @@ bool BlockFilterIndex::CustomRemove(const interfaces::BlockInfo& block)
     // But since this creates new references to the filter, the position should get updated here
     // atomically as well in case Commit fails.
     batch.Write(DB_FILTER_POS, m_next_filter_pos);
-    if (!m_db->WriteBatch(batch)) return false;
+    m_db->WriteBatch(batch);
 
     // Update cached header to the previous block hash
     m_last_header = *Assert(ReadFilterHeader(block.height - 1, *Assert(block.prev_hash)));

src/index/coinstatsindex.cpp

@@ -263,7 +263,7 @@ bool CoinStatsIndex::CustomRemove(const interfaces::BlockInfo& block)
         return false;
     }
 
-    if (!m_db->WriteBatch(batch)) return false;
+    m_db->WriteBatch(batch);
 
     if (!ReverseBlock(block)) {
         return false; // failure cause logged internally

src/index/txindex.cpp

@@ -46,7 +46,8 @@ bool TxIndex::DB::WriteTxs(const std::vector<std::pair<Txid, CDiskTxPos>>& v_pos
     for (const auto& [txid, pos] : v_pos) {
         batch.Write(std::make_pair(DB_TXINDEX, txid.ToUint256()), pos);
     }
-    return WriteBatch(batch);
+    WriteBatch(batch);
+    return true;
 }
 
 TxIndex::TxIndex(std::unique_ptr<interfaces::Chain> chain, size_t n_cache_size, bool f_memory, bool f_wipe)