multi_index: fix compilation failure with boost >= 1.91

This effectively reverts a3cb309e7c from PR #30194.

That PR reduced the multi_index type signatures as recommended upstream, but
this is no longer supported as of boost 1.91 because it is no longer necessary.
1.91 drops support for the pre-c++11 work-arounds that bloated the type
signatures to begin with.

The upstream `BOOST_MULTI_INDEX_ENABLE_MPL_SUPPORT` define is meant to provide
compatibility with removed features, but it does not work for this case. Using
`indexed_by` directly when defining the `multi_index` (as opposed to inheriting
from it) works with all versions, and avoids the use of the back-compat define.

This is a slight regression when building against boost < 1.91 because the
bloated type signatures are reintroduced in that case, but it's not significant
enough to go to the trouble of introducing version detection and ifdefs.

Github-Pull: #35175
Rebased-From: 0bc9d354df

src/node/miner.h

@@ -102,7 +102,9 @@ struct CompareTxIterByAncestorCount {
 };
 
 
-struct CTxMemPoolModifiedEntry_Indices final : boost::multi_index::indexed_by<
+using indexed_modified_transaction_set = boost::multi_index_container<
+    CTxMemPoolModifiedEntry,
+    boost::multi_index::indexed_by<
     boost::multi_index::ordered_unique<
         modifiedentry_iter,
         CompareCTxMemPoolIter
@@ -115,12 +117,7 @@ struct CTxMemPoolModifiedEntry_Indices final : boost::multi_index::indexed_by<
         CompareTxMemPoolEntryByAncestorFee
     >
 >
-{};
-
-typedef boost::multi_index_container<
-    CTxMemPoolModifiedEntry,
-    CTxMemPoolModifiedEntry_Indices
-> indexed_modified_transaction_set;
+>;
 
 typedef indexed_modified_transaction_set::nth_index<0>::type::iterator modtxiter;
 typedef indexed_modified_transaction_set::index<ancestor_score>::type::iterator modtxscoreiter;

src/txmempool.h

@@ -329,7 +329,9 @@ public:
 
     static const int ROLLING_FEE_HALFLIFE = 60 * 60 * 12; // public only for testing
 
-    struct CTxMemPoolEntry_Indices final : boost::multi_index::indexed_by<
+    using indexed_transaction_set = boost::multi_index_container<
+        CTxMemPoolEntry,
+        boost::multi_index::indexed_by<
             // sorted by txid
             boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>,
             // sorted by wtxid
@@ -357,11 +359,7 @@ public:
                 CompareTxMemPoolEntryByAncestorFee
             >
         >
-        {};
-    typedef boost::multi_index_container<
-        CTxMemPoolEntry,
-        CTxMemPoolEntry_Indices
-    > indexed_transaction_set;
+    >;
 
     /**
      * This mutex needs to be locked when accessing `mapTx` or other members

src/txrequest.cpp

@@ -212,17 +212,15 @@ struct ByTimeViewExtractor
     }
 };
 
-struct Announcement_Indices final : boost::multi_index::indexed_by<
-    boost::multi_index::ordered_unique<boost::multi_index::tag<ByPeer>, ByPeerViewExtractor>,
-    boost::multi_index::ordered_non_unique<boost::multi_index::tag<ByTxHash>, ByTxHashViewExtractor>,
-    boost::multi_index::ordered_non_unique<boost::multi_index::tag<ByTime>, ByTimeViewExtractor>
->
-{};
 
 /** Data type for the main data structure (Announcement objects with ByPeer/ByTxHash/ByTime indexes). */
 using Index = boost::multi_index_container<
     Announcement,
-    Announcement_Indices
+    boost::multi_index::indexed_by<
+        boost::multi_index::ordered_unique<boost::multi_index::tag<ByPeer>, ByPeerViewExtractor>,
+        boost::multi_index::ordered_non_unique<boost::multi_index::tag<ByTxHash>, ByTxHashViewExtractor>,
+        boost::multi_index::ordered_non_unique<boost::multi_index::tag<ByTime>, ByTimeViewExtractor>
+    >
 >;
 
 /** Helper type to simplify syntax of iterator types. */