build: Drop libnatpmp from build system

cmake/module/FindNATPMP.cmake

@@ -1,32 +0,0 @@
-# Copyright (c) 2023-present The Bitcoin Core developers
-# Distributed under the MIT software license, see the accompanying
-# file COPYING or https://opensource.org/license/mit/.
-
-find_path(NATPMP_INCLUDE_DIR
-  NAMES natpmp.h
-)
-
-find_library(NATPMP_LIBRARY
-  NAMES natpmp
-)
-
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(NATPMP
-  REQUIRED_VARS NATPMP_LIBRARY NATPMP_INCLUDE_DIR
-)
-
-if(NATPMP_FOUND AND NOT TARGET NATPMP::NATPMP)
-  add_library(NATPMP::NATPMP UNKNOWN IMPORTED)
-  set_target_properties(NATPMP::NATPMP PROPERTIES
-    IMPORTED_LOCATION "${NATPMP_LIBRARY}"
-    INTERFACE_INCLUDE_DIRECTORIES "${NATPMP_INCLUDE_DIR}"
-  )
-  set_property(TARGET NATPMP::NATPMP PROPERTY
-    INTERFACE_COMPILE_DEFINITIONS USE_NATPMP=1 $<$<PLATFORM_ID:Windows>:NATPMP_STATICLIB>
-  )
-endif()
-
-mark_as_advanced(
-  NATPMP_INCLUDE_DIR
-  NATPMP_LIBRARY
-)