Merge bitcoin#19846: build: enable unused member function diagnostic

819d03b refactor: took out unused member functions (Zero)
ed69213 build: enable unused member function diagnostic (Zero)

Pull request description:

  This PR enables the `-Wunused-member-function` compiler diagnostic, as discussed in bitcoin#19702.

  > **Notice**: The `unused-member-function` diagnostic is only available on clang. Therefore, clang should be used to test this PR.

  - [x] Include the `-Wunused-member-function`diagnostic in `./configure.ac`. (ed69213)
  - [x] Resolve the reported warnings. (819d03b)

  Currently, enabling this flag no longer reports the following warnings:

  > **Note**: output from `make 2>&1 | grep "warning: unused member function" | sort | uniq -c`

  ```
  1 index/blockfilterindex.cpp:54:5: warning: unused member function 'DBHeightKey' [-Wunused-member-function]
  2 script/bitcoinconsensus.cpp:50:9: warning: unused member function 'GetType' [-Wunused-member-function]
  1 test/util_tests.cpp:1975:14: warning: unused member function 'operator=' [-Wunused-member-function]
  ```

  All tests have passed locally (from `make check` & `src/test/test_bitcoin`).

  This PR closes bitcoin#19702.

ACKs for top commit:
  practicalswift:
    ACK 819d03b - patch still looks correct :)
  MarcoFalke:
    ACK 819d03b
  pox:
    Tested ACK 819d03b with clang after `make clean`. No unused member function warnings.
  theStack:
    tested ACK 819d03b

Tree-SHA512: 5fdfbbb02b3dc618a90a874a5caa5e01e596fc1d14a209e75a6981f01b253f9bca0cfac8fdd758dd7151986609fb76571c3745124a29cfd4f8cbb8d82a07272e

Author: MarcoFalke

Diff for: configure.ac

@@ -423,6 +423,7 @@ if test "x$CXXFLAGS_overridden" = "xno"; then
   AX_CHECK_COMPILE_FLAG([-Wrange-loop-analysis],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wrange-loop-analysis"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wredundant-decls],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wredundant-decls"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wunused-variable],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wunused-variable"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wunused-member-function],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wunused-member-function"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wdate-time],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wdate-time"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wconditional-uninitialized],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wconditional-uninitialized"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wsign-compare],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wsign-compare"],,[[$CXXFLAG_WERROR]])

Diff for: src/index/blockfilterindex.cpp

@@ -51,7 +51,6 @@ struct DBVal {
 struct DBHeightKey {
     int height;
 
-    DBHeightKey() : height(0) {}
     explicit DBHeightKey(int height_in) : height(height_in) {}
 
     template<typename Stream>

Diff for: src/script/bitcoinconsensus.cpp

@@ -16,8 +16,7 @@ namespace {
 class TxInputStream
 {
 public:
-    TxInputStream(int nTypeIn, int nVersionIn, const unsigned char *txTo, size_t txToLen) :
-    m_type(nTypeIn),
+    TxInputStream(int nVersionIn, const unsigned char *txTo, size_t txToLen) :
     m_version(nVersionIn),
     m_data(txTo),
     m_remaining(txToLen)
@@ -47,9 +46,7 @@ class TxInputStream
     }
 
     int GetVersion() const { return m_version; }
-    int GetType() const { return m_type; }
 private:
-    const int m_type;
     const int m_version;
     const unsigned char* m_data;
     size_t m_remaining;
@@ -84,7 +81,7 @@ static int verify_script(const unsigned char *scriptPubKey, unsigned int scriptP
         return set_error(err, bitcoinconsensus_ERR_INVALID_FLAGS);
     }
     try {
-        TxInputStream stream(SER_NETWORK, PROTOCOL_VERSION, txTo, txToLen);
+        TxInputStream stream(PROTOCOL_VERSION, txTo, txToLen);
         CTransaction tx(deserialize, stream);
         if (nIn >= tx.vin.size())
             return set_error(err, bitcoinconsensus_ERR_TX_INDEX);

Diff for: src/test/util_tests.cpp

@@ -2014,12 +2014,6 @@ struct Tracker
         copies = t.copies + 1;
         return *this;
     }
-    Tracker& operator=(Tracker&& t) noexcept
-    {
-        origin = t.origin;
-        copies = t.copies;
-        return *this;
-    }
 };
 
 }