doc: remove For ... comments

We don't add or maintain these, and they are of little value, as
well as having the effect of polluting diffs.

They are also wrong, i.e DEFAULT_SCRIPTCHECK_THREADS is not in
validation.h.

src/wallet/test/db_tests.cpp

@@ -11,11 +11,16 @@
 #include <wallet/sqlite.h>
 #include <wallet/migrate.h>
 #include <wallet/test/util.h>
-#include <wallet/walletutil.h> // for WALLET_FLAG_DESCRIPTORS
+#include <wallet/walletutil.h>
 
+#include <cstddef>
 #include <fstream>
 #include <memory>
+#include <span>
 #include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
 
 inline std::ostream& operator<<(std::ostream& os, const std::pair<const SerializeData, SerializeData>& kv)
 {