remove cryptopp, enet from builtins

Index: externals/CMakeLists.txt
--- externals/CMakeLists.txt.orig
+++ externals/CMakeLists.txt
@@ -9,33 +9,8 @@ set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${PROJECT_S
 include(DownloadExternals)
 include(ExternalProject)
 
-# Boost
-set(BOOST_ROOT "${CMAKE_SOURCE_DIR}/externals/boost")
-set(Boost_INCLUDE_DIR "${CMAKE_SOURCE_DIR}/externals/boost")
-set(Boost_NO_SYSTEM_PATHS ON)
-add_library(boost INTERFACE)
-target_include_directories(boost SYSTEM INTERFACE ${Boost_INCLUDE_DIR})
-
-# Boost::serialization
-file(GLOB boost_serialization_SRC "${CMAKE_SOURCE_DIR}/externals/boost/libs/serialization/src/*.cpp")
-add_library(boost_serialization STATIC ${boost_serialization_SRC})
-target_link_libraries(boost_serialization PUBLIC boost)
-
 # Add additional boost libs here; remember to ALIAS them in the root CMakeLists!
 
-# Catch2
-set(CATCH_INSTALL_DOCS OFF)
-set(CATCH_INSTALL_EXTRAS OFF)
-add_subdirectory(catch2)
-
-# Crypto++
-add_subdirectory(cryptopp)
-
-# fmt and Xbyak need to be added before dynarmic
-# libfmt
-option(FMT_INSTALL "" ON)
-add_subdirectory(fmt)
-
 # Xbyak
 if ("x86_64" IN_LIST ARCHITECTURE)
     add_subdirectory(xbyak)
@@ -89,10 +64,6 @@ set(ZSTD_BUILD_PROGRAMS OFF)
 set(ZSTD_BUILD_SHARED OFF)
 add_subdirectory(zstd/build/cmake EXCLUDE_FROM_ALL)
 target_include_directories(libzstd_static INTERFACE $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/externals/zstd/lib>)
-
-# ENet
-add_subdirectory(enet)
-target_include_directories(enet INTERFACE ./enet/include)
 
 # Cubeb
 if (ENABLE_CUBEB)