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/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